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MINERALOGY 

AN  INTRODUCTION  TO  THE  STUDY  OF 
MINERALS  AND  CRYSTALS 


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MINERALOGY 

AN  INTRODUCTION  TO  THE  STUDY 

OF 

MINERALS  AND  CRYSTALS 


BY 
EDWARD  HENRY  KRAUS,  PH.D.,  Sc.D. 

PROFESSOR   OF   CRYSTALLOGRAPHY   AND   MINERALOGY   AND   DIRECTOR   OF   THE   MINERALOGICAL 
LABORATORY,   UNIVERSITY   OT   MICHIGAN 


AND 


WALTER  FRED  HUNT,  PH.D. 

ASSOCIATE   PROFESSOR   OF   MINERALOGY   AND   PETROGRAPHY, 
UNIVERSITY   OF   MICHIGAN 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 

NEW  YORK:    239   WEST  39TH  STREET 

LONDON:    6  &  8  BOUVERIE  ST.,  E.  C.  4 

1920 


SCIENO 
UBRAR 


COPYRIGHT,  1920,  BY  THE 
McGRAw-HiLL  BOOK  COMPANY,  INC. 


MAPLK    PRESS    T  O  R  K    PA 


PREFACE 

This  text  is  the  result  of  long  experience  in  teaching  large  classes  of 
beginning  students,  and  the  subject  is  accordingly  presented  in  a  direct 
and  simple  manner.  The  essentials  of  the  various  phases  of  the  science 
have  been  treated  so  that  a  single  book  may  serve  the  needs  of  the  aver- 
age student.  The  conventional  line  drawings  of  crystals,  which  students 
commonly  have  difficulty  in  properly  visualizing,  have  been  super- 
seded to  a  very  large  extent  by  excellent  photographs  of  crystal  models, 
natural  crystals,  and  minerals,  such  as  are  actually  handled  in  the 
laboratory.  These  are  all  original  photographs  of  material  contained  in 
the  various  collections  of  the  University  of  Michigan. 

Furthermore,  an  attempt  has  been  made  to  vitalize  the  subject  as 
much  as  possible,  and  accordingly  there  are  chapters  on  the  importance  of 
mineralogy  in  modern  civilization,  on  gems  and  precious  stones,  and  on 
the  production  and  uses  of  the  important  economic  minerals.  Numerous 
photographs  and  short  sketches  of  distinguished  mineralogists  have  also 
been  introduced  in  the  hope  that  they  will  add  «,  human  touch. 

The  chapters  on  crystallography  are  based  very  largely  upon  the 
senior  author's  Essentials  of  Crystallography,  while  much  of  the  material 
in  the  descriptions  of  the  150  minerals  given  in  this  text  has  been  taken 
from*  his  Descriptive  Mineralogy.  The  determinative  tables  are  an 
abridgment  of  the  authors'  Mineral  Tables. 

We  are  greatly  indebted  to  Mr.  George  R.  Swain,  technical  expert 
in  photography  in  the  University  of  Michigan,  whose  varied  experience 
and  unusual  skill  made  the  excellent  photographs  of  models  and  minerals 
possible;  also  to  Dr.  George  F.  Kunz  for  valuable  assistance  in  securing 
a  considerable  number  of  very  desirable  photographs. 

EDWARD  H.  KRAUS. 
WALTER  F.  HUNT. 
MlNERALOGICAL  LABORATORY, 
UNIVERSITY  OF  MICHIGAN, 
August,  1920. 


427653 


CONTENTS 

PAGE 

INTRODUCTION vii 

CHAPTER 

I.  CRYSTALLOGRAPHY 1 

II.  CUBIC  SYSTEM ^ 14 

III.  HEXAGONAL  SYSTEM.    .    .    .  ^. 30 

IV.  TETRAGONAL  SYSTEM  ....  V 55 

V.  ORTHORHOMBIC  SYSTEM  .    .   71 65 

VI.  MONOCLINIC  SYSTEM.    .    .    .  o. 72 

VII.  TRICLINIC  SYSTEM ^ 78 

VIII.  COMPOUND  CRYSTALS 82 

IX.  PHYSICAL  PROPERTIES.    ,.......- 88 

X.  THE  POLARIZING  MICROSCOPE 99 

XI.  CHEMICAL  PROPERTIES.    . 125 

XII.  FORMATION  AND  OCCURRENCE  OP  MINERALS 131 

XIII.  QUALITATIVE  BLOWPIPE  METHODS.    ,    .    .   C 145 

XIV.  DESCRIPTIVE  MINERALOGY .    .   ,    .    . 186 

1.  Elements • 187 

2.  Sulphides,  Arsenides,  and  Sulpho-minerals 202 

3.  Oxides  and  Hydroxides 219 

4.  Haloids 236 

5.  Nitrates,  Carbonates,  and  Manganites 240 

6.  Sulphates,  Chromates,  Molybdates,  Tungstates,  and  Uranates  .    .    .  254 

7.  Aluminates,  Ferrites,  and  Borates 267 

8.  Phosphates,  Columbates,  and  Vanadates 272 

9.  Silicates  and  Titanites 277 

XV.  GEMS  AND  PRECIOUS  STONES 329 

XVI.  CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS 339 

GLOSSARY .  366 

TABULAR  CLASSIFICATION  OF  THE  THIRTY-TWO  CLASSES  OF  SYMMETRY 372 

TABLES  FOR  THE  DETERMINATION  OF  MINERALS 379 

INDEX.                                                                                                                               .  549 


vu 


INTRODUCTION 

Mineralogy  and  Civilization. — The  older  classifications  of  natural 
history  commonly  referred  substances  occurring  in  nature  to  the  animal, 
vegetable,  or  mineral  kingdoms.  The  first  of  these  kingdoms  considered 
the  animal  life  on  land,  in  the  sea,  and  in  the  air,  and  from  a  study  of 
these  animal  forms  there  has  been  developed  zoology  with  its  host  of 
allied  sciences,  such  as  anatomy,  surgery,  animal  breeding,  and  so  forth. 
The  second  kingdom  included  the  plants  and  trees,  and  the  study  of  these 
has  given  us  the  science  of  botany  and  such  closely  related  subjects  as 
forestry  and  agriculture.  The  mineral  kingdom,  in  the  opinion  of  the 
ancients,  included  the  whole  inanimate  world;  in  short,  minerals,  rocks, 
soil,  and  the  "  waters  of  the  earth."  Inasmuch  as  bright  colors,  regu- 
larity of  form,  transparency,  and  other  prominent  properties  have 
always  attracted  attention,  there  is  little  wonder  that  minerals  with 
their  great  diversity  of  colors  and  form  should  have  been  among  the 
first  objects  studied  by  primitive  man. 

Although  mineralogy  as  a  science  is  comparatively  young,  minerals 
and  crystals  were  nevertheless  used  very  early  in  the  development 
of  civilization.  In  fact,  the  earliest  stage  in  the  development  of  civiliza- 
tion is  commonly  referred  to  as  the  stone  age.  In  this  age  rocks  or 
stones  were  hewn  into  numerous  shapes  and  used  for  utensils  of  various 
kinds.  They  were  also  made  into  crude  weapons.  At  first  the  stones 
were  for  the  most  part  rough,  but  subsequently  methods  were  devised 
so  that  they  could  be  rendered  smooth  and  polished  to  some  extent. 
Therefore  this  period  is  frequently  divided  into  the  rough  and  smooth 
stone  ages,  the  paleolithic  and  neolithic  ages,  respectively. 

As  his  knowledge  of  rocks  and  minerals  increased  and  he  was  able 
to  recover  metals  from  the  rocks,  man  emerged  successively  into  the 
copper,  bronze,  iron,  and  coal  ages.  The  present  day  is  commonly 
called  the  motor  age,  a  motor  being  an  assemblage  of  metals.  Indeed, 
as  our  civilization  becomes  more  advanced  and  complex,  the  demand 
for  metals  of  all  sorts  and  hence  for  minerals  ever  increases. 

Sources  of  Raw  Materials. — The  principal  sources  of  raw  materials 
are;  the  mines  and  quarries,  the  farms,  the  forests,  the  sea,  and  the 
atmosphere.  Of  these,  the  farms,  forests,  and  the  mines  and  quarries 
are  the  greatest  contributors. 

Divisions  of  Human  Activity. — Upon  the  exploitation  of  these  natural 
resources  rest  the  greatest  and  most  important  divisions  of  human  activ- 
ity, namely,  agriculture,  mining,  and  commerce  and  industry.  As  is 
well  known,  agriculture  furnishes  us  with  many  of  the  products  so 


x  INTRODUCTION 

necessary  to  our  sustenance;  that  is,  with  the  cereals  and  other  crops. 
Indirectly,  it  gives  us  much  of  our  meat  products,  wearing  apparel,  and 
the  like.  However,  in  order  to  carry  on  agriculture  with  marked  success, 
a  knowledge  of  the  composition  and  nature  of  soils  is  absolutely  essential. 
Soils,  however,  consist  of  minerals  and  mineral  products  to  a  very  large 
extent.  Indeed,  all  balanced  soils  suited  to  general  cropping  contain  a 
preponderance  of  mineral  matter. 

It  is  obvious  that  in  mining  a  most  comprehensive  knowledge  of 
mineralogy  is  necessary.  In  many  localities,  mining  is  by  far  the  chief 
occupation.  Indeed,  as  Del  Mar  says,  "  Desire  for  the  precious  metals, 
rather  than  geographical  researches  or  military  conquest,  is  the  principal 
motive  which  has  led  to  the  dominion  of  the  earth  by  civilized  races. 
Gold  has  invariably  invited  commerce,  invasion  has  followed  commerce, 
and  permanent  occupation  has  completed  the  process."  Several  com- 
paratively recent  instances  will  be  cited.  The  stimulus  given  to  world- 
wide migration  and  trade  by  the  discovery  of  gold  in  California  in 
1849  is  well  known.  For  gold,  Englishmen  began  to  populate  antipodal 
Australia  in  1850.  The  discovery  of  diamonds  near  Kimberley  in  1867 
and  of  gold  in  the  Rand  district  in  1885  led  to  the  subsequent  settlement  of 
large  sections  of  South  Africa.  Alaska  came  into  prominence  only  after 
the  discovery  of  gold  and  other  valuable  minerals  late  in  the  nineties. 

Mining  is  often  the  fore-runner  of  agriculture.  It  is  also  to  a  large 
extent  the  basis  of  commerce  and  industry.  In  fact,  commerce  and 
industry  may  be  said  to  rest  in  general  upon  agriculture  and  mining. 
The  exploitation  of  valuable  mineral  deposits  leads  invariably  to  the 
development  of  lines  of  transportation  and  communication.  Thus,  the 
principal  commerce  of  the  Great  Lakes  consists  of  carrying  enormous 
quantities  of  iron  ore  from  the  Lake  Superior  region  to  various  points 
on  the  lower  lakes  and  of  transporting  coal  from  these  ports  on  the  return 
trip.  Likewise,  many  of  the  industries  in  the  vicinity  of  the  Great  Lakes 
are  directly  dependent  upon  mining  in  that  they  utilize  the  products  of 
the  mines  and  quarries.  Furthermore,  conservative  estimates  show  that 
nearly  two-thirds  of  the  total  traffic  of  our  railroads  consists  of  the  carry- 
ing of  minerals  and  mineral  products. 

The  Nation  and  its  Mineral  Resources. — The  importance  of  a  nation's 
resources  has  been  emphasized  by  the  World  War.  Indeed,  the  mineral 
resources  of  a  nation  are  now  recognized  as  one  of  its  foundations  of 
power  and  are  considered  among  its  most  valuable  assets.  The  great 
contributions  of  the  United  States  in  the  winning  of  the  war  consisted 
largely  in  supplying  enormous  quantities  of  materials  that  were,  directly 
or  indirectly,  the  products  of  the  mines  or  of  the  soil.  This  was  to  be 
expected  of  a  country  which  under  normal  conditions  produces  60  per  cent, 
of  the  world's  copper,  40  per  cent,  of  the  iron,  32  per  cent,  of  its  lead  and 
zinc,  66  per  cent,  of  the  petroleum,  40  per  cent,  of  its  coal,  72  per  cent,  of 


INTRODUCTION  xi 

the  corn,  20  per  cent,  of  the  wheat,  and  60  per  cent  of  its  cotton.  Direc- 
tor G.  O.  Smith  of  the  United  States  Geological  Survey  says:  "  Independ- 
ence through  possession  of  the  material  resources  essential  to  modern  life 
is  itself  a  promise  of  a  nation's  integrity,  and  the  nation  that  makes 
the  whole  world  its  debtor  through  shipments  of  the  mineral  fuels 
and  the  metals  and  the  mineral  fertilizers  occupies  a  strategic  position 
in  the  construction  of  international  policy." 

Relation  of  Mineralogy  to  Other  Sciences. — Mineralogy,  then,  must 
be  considered  as  a  subject  which  is  fundamental  to  a  large  extent.  It 
is  a  subject  of  vital  importance  to  many  types  of  students,  among  whom 
mention  may  be  made  of  students  of  geology,  chemistry,  pharmacy, 
physics,  forestry,  soils,  and  engineering,  not  to  include  those  looking 
forward  to  mineralogy  as  a  profession. 

The  geologist  whose  task  it  is  to  observe  and  interpret  the  processes 
which  are,  and  have  been,  at  work  upon  the  earth,  should  be  well  grounded 
in  mineralogy,  for  the  earth  consists  largely  of  rocks  which  in  turn 
are  made  up  of  minerals.  The  chemist  and  the  pharmacist  are  deal- 
ing to  a  large  extent  with  raw  materials  which  consist  of  minerals. 
Many  of  the  important  chemical  processes  are  dependent  wholly  or 
in  part  upon  the  use  of  minerals.  This  is  especially  true  of  inor- 
ganic chemistry.  Thus,  the  well-known  Solvay  process  for  the  manu- 
facture of  the  alkalies  uses  as  raw  materials — limestone,  halite  or 
common  salt,  and  coal — products  of  the  mines  or  quarries.  More- 
over, it  has  recently  been  shown  that  the  synthetic  compounds  of 
the  organic  chemist  and  the  alkaloids  of  the  pharmacist  can  in  very 
many  instances  be  rapidly  determined  by  the  use  of  refined  optical 
methods  which  have  been  devised  by  the  mineralogist. 

Many  of  the  important  laws  in  physics,  especially  those  relating 
to  the  properties  of  light,  have  been  studied  principally  on  crystallized 
minerals.  The  Nobel  prizes  in  physics  for  1914  and  1915  were  awarded 
to  Laue  and  the  Braggs  (father  and  son)  for  epoch  making  investigations 
upon  the  structure  of  crystallized  minerals  by  means  of  the  #-ray. 

In  this  country,  the  forester  and  the  student  of  soils  very  frequently 
are  at  work  in  new  and  undeveloped  sections.  In  their  field  surveys, 
they  are  able  to  recognize  at  a  glance  the  character  of  the  soil  and  of  the 
rock  exposures.  They  should  further  be  able  to  pass  fairly  accurate 
judgment  upon  the  possible  value  of  any  minerals  or  ore  deposits  they 
find.  In  order  to  do  this,  some  knowledge  of  mineralogy  is  required. 

In  railroad,  highway,  and  waterway  construction,  the  engineer  is 
constantly  encountering  problems  which  involve  a  knowledge  of  miner- 
alogy. As  in  the  case  of  the  forester  and  the  student  of  soils,  he  is 
frequently  working  in  undeveloped  sections  of  the  country.  Some  of  our 
most  valuable  ore  deposits  have  been  discovered  as  the  direct  result  of 
railroad  building.  The  great  mineral  deposits  at  Sudbury,  Ontario, 


Xll 


INTRODUCTION 


which  now  furnish  such  enormous  quantities  of  nickel,  and  the  valuable 
silver  mines  at  Cobalt,  Ontario,  to  mention  two  recent  examples  only, 
were  discovered  in  this  way. 

History    of    Mineralogy.  —  Mineralogy  is  a    comparatively    young 
science,  having  been  developed  more  recently  than  astronomy,  chemistry, 

mathematics,  or  physics.  Although  minerals 
and  metals  were  frequently  used  by  the 
ancients,  the  first  extensive  work  on  miner- 
alogy did  not  appear  until  1546,  when  Georg 
Agricola  published  his  De  Natura  Fossilium. 
It  is  commonly  conceded  that  Werner  (1750- 
1817),  for  many  years  a  professor  in  the 
famous  school  of  mines  at  Freiburg,  Saxony, 
was  the  first  to  place  mineralogy  upon  a 
scientific  basis.  At  first,  mineralogy  and 
geology  were  not  differentiated,  and  only  in 
comparatively  recent  times  have  they  been 
recognized  as  distinct  sciences. 

Minerals  and  Rocks. — The  exterior  of  the 
earth  is  made  up  of  solids,  liquids,  and  oc- 
cluded gases.  The  solids  are  commonly 
called  rocks.  It  is  with  these  that  we  are 
concerned.  Let  us  consider  the  general  characterstics  of  several  of  the 
most  common  rocks.  In  examining  a  granite,  for  example  (Fig.  2),  it 
is  at  once  seen  that  it  is  heterogeneous  in  character;  that  is,  it  is  made 
up  of  several  constituents.  In  general,  there  is,  first,  a  colorless/granu- 
lar, and  glassy  material  which  is  called  quartz;  second,  a  whitish  sub- 
stance with  rather  even  surfaces,  known  as  feldspar;  and  third,  a  dark 


FIG.  1. — Abraham  G.  Wer- 
ner (1750-1817)  pioneer  min- 
eralogist. 


I 


FIG.  3.— Syenite.         FIG.  4.— Sandstone.        FIG.  5.— Marble. 


colored  and  scaly  material,  which  is  commonly  designated  as  mica. 
If  these  three  crystalline  constituents  are  analyzed,  it  will  be  noted 
that  characteristic  chemical  compositions  can  be  assigned  to  them. 
Thus,  quartz,  SiO2,  feldspar,  KAlSi3O8,  and  mica,  KHMg2Al2Si8Oi2. 
In  examining  another  common  rock  such  as  syenite  (Fig.  3)  it  will  be 
found  that  it  is  quite  frequently  composed  of  two  constituents — mica 
and  feldspar.  On  the  other  hand,  such  rocks  as  sandstone  (Fig.  4) 


INTRODUCTION 


Xlll 


and  marble  (Fig.  5)  consist  of  one  component  only,  quartz  and  calcite, 
CaCO3,  respectively.  When  these  substances  are  studied,  it  is  fre- 
quently found  that  they  occur  in  regular  forms;  that  is,  they  are  bounded 
by  natural  plane  surfaces.  These  rock  constituents  are  minerals. 

Definition  of  a  Mineral. — A  mineral,  then,  may  be  defined  as  a 
substance  occurring  in  nature  with  a  characteristic  chemical  composition, 
and  usually  possessing  a  definite  crystalline  structure,  which  is  sometimes 
expressed  in  external  geometrical  forms  or  outlines.  Characteristic  of  a 
mineral  is  its  occurrence  in  nature. 
The  same  chemical  substance,  for  ex- 
ample CaSO4,  may  be  found  in  nature 
or  may  be  prepared  in  the  chemical 
laboratory.  When  found  in  nature  it  is 
designated  as  a  mineral  and  has  a  spe- 
cial mineralogical  name  assigned  to  it, 
anhydrite  (Fig.  6).  When  prepared  in 
the  laboratory  it  cannot  be  interpreted 
as  a  mineral  and  is  usually  referred  to 
as  calcium  sulphates  Therefore,  in 
order  to  be  classified  as  a  mineral,  a 
substance  must  be  the  product  of  nature  and  not  the  result  of  processes 
carried  on  in  the  laboratory.  Most  minerals  are  inorganic  in  character 
and  are  either  chemical  elements  or  combinations  of  such  elements; 
that  is,  chemical  compounds.  Some  substances  of  an  organic  nature, 
such  as  coal,  amber,  petroleum,  asphalt,  and  so  forth,  are  frequently 
included.  As  indicated,  a  few  minerals  are  very  simple  in  composition, 
such  as  sulphur,  silver,  copper,  and  gold.  These  are  elements. 


FIG.  6. — Anhydrite,  oakwood  salt 
shaft,  Detroit,  Michigan. 


•ML! 


FIG.  7. — Calcite.     Joplin, 
Missouri. 


FIG.  8. — Quartz.     Dauphine,  France. 


Crystals. — When  minerals  occur  with  definite  geometrical  outlines 
they  are  called  crystals  (Figs.  7  and  8).     Unlike  minerals,  crystals  may 


xiv  INTRODUCTION 

be  the  result  of  processes  carried  on  either  in  nature  or  in  the  laboratory. 
They  are  solids  bounded  by  natural  plane  surfaces  called  crystal  faces. 
Many  minerals  are  found  as  excellent  crystals.  Accurate  and  rapid 
determination  of  minerals  can,  in  many  cases,  be  most  successfully 
made  by  recognizing  the  crystal  form.  Crystallography  is  the  science 
which  deals  with  the  form  and  various  properties  of  crystals.  A  knowl- 
edge of  the  essentials  of  geometrical  crystallography  is  absolutely 
indispensible  in  the  rapid  determination  of  minerals. 

Divisions  of  Mineralogy.— An  elementary  course  in  mineralogy  may 
be  conveniently  divided  into  (1)  crystallography,  (2)  physical  mineralogy, 
(3)  chemical  mineralogy,  (4)  descriptive  mineralogy,  (5)  determina- 
tive mineralogy. 

Crystallography. — This  portion  of  the  text  aims  to  make  the  student 
familiar  with  the  common  crystal  forms  exhibited  by  minerals,  first  by 
the  study  of  crystal  models  and  later  by  the  recognition  of  the  various 
forms  exhibited  by  natural  crystals. 

Physical  Mineralogy. — This  includes  the  consideration  of  the  various 
physical  properties  such  as  hardness,  cleavage,  color,  luster,  streak, 
specific  gravity,  as  well  as  the  various  optical  properties  of  crystallized 
minerals.  The  study  of  the  properties  last  referred  to  involves  the  use 
of  the  mineralogical  or  polarizing  microscope. 

Chemical  Mineralogy. — In  this  chapter  the  various  chemical  prop- 
erties of  minerals,  and  also  their  origin  and  formation,  will  be  considered. 
The  determination  of  their  chemical  constituents,  especially  by  blowpipe 
methods,  will  be  treated  in  detail. 

Descriptive  Mineralogy. — In  this  chapter  one-hundred  and  fifty  of  the 
most  common  minerals  will  be  described  as  to  their  crystallography, 
chemical  and  physical  properties,  occurrences  and  associates,  and  uses. 
There  will  also  be  included  sections  relating  to  the  use  of  minerals  as  pre- 
cious stones,  statistics  of  mineral  production  and  uses,  and  the  classifica- 
tion of  minerals  according  to  their  important  chemical  constituents. 

Determinative  Mineralogy. — For  the  purpose  of  acquiring  facility 
in  the  rapid  recognition  of  minerals  by  means  of  their  physical  properties, 
pages  380  to  547  contain  determinative  tables  for  the  one  hundred  and 
fifty  minerals  described  in  this  text. 


MINERALOGY 


AN  INTRODUCTION  TO  THE  STUDY  OF  MINERALS 
AND  CRYSTALS 


CHAPTER  I 
CRYSTALLOGRAPHY 

Subdivisions  of  Crystallography. — This  science  treats  of  the  various 
properties  of  crystals  and  crystallized  bodies.  It  may  be  subdivided  as 
follows : 

1.  Geometrical  Crystallography. 

2.  Physical  Crystallography. 

3.  Chemical  Crystallography. 

Geometrical  crystallography,  as  the  term  implies,  describes  the  various 
forms  occurring  upon  crystals.  The  relationships  existing  between  the 
crystal  form  and  the  physical  and  chemical  properties  of  crystals  are  the 
subjects  of  discussion  of  the  second  and  third  subdivisions  of  this  science, 
respectively.  In  order  to  be  able  to  determine  minerals  rapidly  at  least, 
the  essentials  of  geometrical  crystallography  must  have  been  mastered. 

Constancy  of  Interfacial  Angles. — In  general,  crystals  may  result  from 
solidification  from  a  solution,  state  of  fusion,  or  vapor.  Let  us  suppose 


FIG.  9. 


FIG.   10. 


FIG.   11. 


that  some  ammonium  alum,  (NH^AWSO^^HaO,  has  been  dissolved 
in  water  and  the  solution  allowed  to  evaporate  slowly.  As  the  alum 
begins  to  crystallize,  it  will  be  noticed  that  the  crystals  are,  for  the  most 
part,  bounded  by  eight  plane  surfaces.  If  these  surfaces  are  all  of  the 
same  size,  that  is,  equally  developed,  the  crystals  will  possess  an  outline 

1 


MINERALOGY 


as  repres&tited  by  Pig:  9^  ^Stcb' a  form  is  termed  an  octahedron.     The 
octahedron  is  bounded  by  eight  equilateral  triangles.     The  angles  be- 


FIG.  12. 


FIG.   13. 


FIG.   14. 


tween  any  two  adjoining  surfaces  or  faces,  as  they  are  often  called,  is  the 
same,  namely,  109°  28^'.     On  most  of  the  crystals,  however,  it  will  be 

seen  that  the  various  faces  have  been  developed 
unequally,  giving  rise  to  the  forms  illustrated 
by  Figs.  10  and  11.  Similar  cross-sections 
through  these  forms  are  shown  in  Figs.  12, 
13,  and  14,  and  it  is  readily  seen  that,  although 
the  size  of  the  faces  and,  hence,  the  resulting 
shapes  have  been  materially  changed,  the  angle 
between  the  adjoining  faces  has  remained  the 
same,  namely,  109°  28 y±  .  Such  forms  of  the 
octahedron  are  said  to  be  misshapen  or  dis- 
torted. Distortion  is  quite  common  on  all 
crystals  regardless  of  their  chemical  composi- 
tion. 

It  was  the  Danish  physician  and  natural 
scientist,  Nicolaus  Steno,  (Fig.  15)  who  in 
1669  first  showed  that  the  angles  between  similar  faces  on  crystals  of 
quartz  remain  constant  regardless  of  their  development.  Figures  16 


FIG.  15.  —  Nicolaus 
Steno  (1638-1687).  Dis- 
coverer of  the  law  of  the 
constancy  of  interfacial 
angles. 


FIG.   16. 


FIG.   17 


and   17   represent   two  crystals  of   quartz   with   similar   cross-sections 
(Figs.   18  and  19).     Further  observations,  however,  showed  that  this 


CRYSTALLOGRAPHY 


applies  not  only  to  quartz  but  to  all  crystallized  substances  and,  hence, 
we  may  state  the  law  as  follows:  Measured  at  the  same  temperature, 
similar  angles  on  crystals  of  the^same  substance  remain  constant  regardless  of 
the  size  or  shape  of  the  crystal. 

Crystal  Habit. — The  various  shapes  of  crystals,  resulting  from 
the  unequal  development  of  their  faces,  are  often  called  their 
habits.  Figures  9,  10,  and  11  show  some  of  the  habits  assumed  by  alum 


FIG.   18. 


FIG.   19. 


crystals.  In  Fig.  9,  the  eight  faces  are  about  equally  developed  and  this 
may  be  termed  the  octahedral  habit.  The  tabular  habit,  Fig.  10,  is  due 
to  the  predominance  of  two  parallel  faces.  Figure  11  shows  four  parallel 
faces  predominating,  and  the  resulting  form  is  the  prismatic  habit 

Crystallographic  Axes. — Inasmuch  as  the  crystal  form  of  any  sub- 
stance is  dependent  upon  its  physical  and  chemical  properties,  it 
necessarily  follows  that  an  almost  infinite  variety  of  forms  is  possible. 
In  order,  however,  to  study  these  forms  and  define  the  position  of  the 


FIG.  20. 


-c 

FIG.  21. 


faces  occurring  on  them  advantageously,  straight  lines  are  assumed  to 
pass  through  the  ideal  center  of  each  crystal.  These  lines  are  the  crystal- 
lographic  axes.  Their  intersection  forms  the  axial  cross.  Figure  20  shows 
the  octahedron  referred  to  its  three  crystal  axes.  In  this  case  the  axes 
are  of  equal  length  and  termed  a  axes.  The  extremities  of  the  axes 
are  differentiated  by  the  use  of  the  plus  and  minus  signs,  as  shown  in 
Fig.  20. 


MINERALOGY 


If  the  axes  are  of  unequal  lengths,  the  one  extending  from  front  to  rear 
is  termed  the  a  axis,  the  one  from  right  to  left  the  b,  while  the  vertical 
axis  is  called  the  c  axis.  This  is  illustrated  by  Fig.  21.  The  axes  are 
always  referred  to  in  the  following  order,  viz. :  a,  6,  c. 

Crystal  Systems. — Although  a  great  variety  of  crystal  forms  is 
possible,  it  has  been  shown  in  many  ways  that  all  forms  may  be  classified 
into  six  large  groups,  called  crystal  systems.  In  the  grouping  of  crystal 
forms  into  systems,  we  are  aided  by  the  crystallographic  axes.  The 
systems  may  be  differentiated  by  means  of  the  axes  as  follows: 

1.  Cubic  System. — Three  axes,  all  of  equal  lengths,  intersect  at  right 
angles.    The  axes  are  designated  by  the  letters,  a,  a,  a. 

2.  Hexagonal  System. — Four  axes,  three  of  which  are  equal  and  in  a 
horizontal  plane  intersecting  at  angles  of  60°.    These  three  axes  are 
often  termed  the  lateral  axes,  and  are  designated  by  a,  a,  a.    Perpen- 
dicular to  the  plane  of  the  lateral  axes  is  the  vertical  axis,  which  may  be 
longer  or  shorter  than  the  a  axes.    This  fourth  axis  is  called  the  principal 
or  c  axis. 


FIG.  22. 


3.  Tetragonal  System. — Three  axes,  two  of  which  are  equal,  horizontal, 
and  perpendicular  to  each  other.     The  vertical,  c,  axis  is  at  right  angles 
to  and  either  longer  or  shorter  than  the  horizontal  or  lateral,  a,  axes. 
The  vertical  axis  is  often  called  the  principal  axis. 

4.  Orthorhombic  System. — Three  axes  of  unequal  lengths  intersect  at 
right  angles.     These  axes  are  designated  by  a,  6,  c,  as  shown  in  Fig.  21. 

5.  Monoclinic  System. — Three  axes,  all  unequal,  two  of  which  (a,  c) 
intersect  at  an  oblique  angle,  the  third  axis  (b)  being  perpendicular  to 
these  two. 

6.  Triclinic  System. — Three  axes  (a,  6,  c,)  are  all  unequal  and  intersect 
at  oblique  angles. 

Parameters  and  Parametral  Ratio. — In  order  to  determine  the  posi- 
tion of  a  face  on  a  crystal,  it  must  be  referred  to  the  crystallographic 
axes.  Figure  22  shows  an  axial  cross  of  the  orthorhombic  system.  The 
axes,  a,  6,  c,  are,  therefore,  unequal  and  perpendicular  to  each  other. 
The  plane  ABC  cuts  the  three  axes  at  the  points  A,  B,  and  C,  hence,  at 


CRYSTALLOGRAPHY 


the  distance  OA  =  a,  OB  =  b,  OC  =  c,  from  the  center,  0.  These  distances, 
OA,  OB,  and  OC,  are  known  as  the  parameters  and  the  ratio,  OA  :  OB  : 
OC,  as  the  parametral  ratio  of  the  plane  ABC.  This  ratio  may  be  abbre- 
viated to  a  :  b  :  c. 

There  are,  however,  seven  other  planes  possible  about  this  axial 
cross  which  possess  parameters  of  the  same  lengths  as  those  of  the  plane 
ABC,  Fig.  23.  The  simplified  ratios  of  these  planes  are: 


a 

-b 

c 

a 

b 

-c 

a 

-b 

-c 

-a 

b 

c 

-a 

-b 

c 

—a 

b 

-c 

—a 

-b 

-c 

These  eight  planes  are  all  similarly  located  with  respect  to  the  crystal- 
ographic  axes.  They  constitute  a  crystal  form,  and  may  be  represented 
by  the  general  ratio  (a  :b  :  c).  The  number  of 
faces  in  a  crystal  form  depends,  moreover,  not 
only  upon  the  intercepts  or  parameters  but  also 
upon  the  elements  of  symmetry  possessed  by 
the  crystal,  see  page  10.  Those  forms,  which 
enclose  space,  are  called  closed  forms.  Figure 


FIG.  24. 


FIG.  25. 


23  is  su«h  a  form.     Those,  however,  which  do  not  enclose  space  on  all 
sides,  as  shown  in  Fig.  24,  are  termed  open  forms. 

Fundamental  and  Modified  Forms. — In  Fig.  25,  the  enclosed  form 
possesses  the  general  ratio,  a  :  b  :  c.  The  face  ABM,  however,  has  the 
parametral  ratio,  oA  :  oB  :  oM,  where  oA  =  a,  oB  =  b,  and  oM  =  3oC  = 
3c.  Hence,  this  ratio  may  be  written  a  :  b  :  3c.  But,  as  in  the  previous 
case,  this  ratio  represents  a  form  consisting  of  eight  faces  as  shown  in  the 
figure.  That  form,  the  parameters  of  which  are  selected  as  the  unit 


0  MINERALOGY 

lengths  of  the  crystallographic  axes,  is  known  as  the  unit  or  fundamental 
form  In  Fig.  25  the  inner  bipyramid,  or  double  pyramid,  is  a  so-called 
unit,  whereas  the  outer  is  a  modified  form. 

Combinations. — Several  different  forms  may  occur  simultaneously 
upon  a  crystal,  giving  rise  to  a  combination.  Figures  26  and  27  show  a 
combination  of  two  bipyramids  observed  on  sulphur;  p  =  a  :  b  :  c 


FIG.  26. 


FIG.  27. 


FIG.  28.  FIG.  29. 

(unit)  and  s  =  a  :  b  :  ^c  (modified).     Figures  28  and  29  shows  the  two 
forms,  o  =  a  :  a  :  a,  and  h  =  a  :  <*>a  :  &>a,  see  page  16. 

Axial  Ratio. — If  the  intercepts  of  a  unit  form  cutting  all  three  axes 
be  expressed  in  figures,  the  intercept  along  the  b  axis  being  considered 
as  unity,  we  obtain  the  axial  ratio.  In  Figs.  26  and  27,  which  represent 
a  crystal  of  sulphur,  the  axial  ratio  is: 

a  :b  :c  =  0.8131  :  1  :  1.9034. 

Every  crystallized  substance  has  its  own  axial  ratio.  This  is  illus- 
trated by  the  ratios  of  three  minerals  crystallizing  in  the  orthorhombic 
system. 


Aragonite,  CaCO3,  a  :  b 

Anglesite,  PbSO4,  a  :  b 

Topaz,  A12(F.OH)2  SiO4,  (i  ;  fr 


c  =  0.6228  :  1  :  0.7204 
c  =  0.7852  :  1  :  1.2894 
c  =  0.5281  :  1  :  0.9442 


CRYSTALLOGRAPHY 


In  the  hexagonal  and  tetragonal  systems,  since  the  horizontal  axes 
are  equal,  i.e.,  a  =  6,  see  page  4,  the  axial  ratio  is  reduced  to  a  :  c;  a 
now  being  unity.  Thus,  the  axial  ratio  of  zircon  (ZrSiO4)  which  is  tetra- 
gonal, may  be  expressed  as  follows:  a  :c  =  1  : 0.6404;  that  of  quartz 
(SiO2),  hexagonal,  by  a  :  c  =  1  :  1.0999.  Obviously,  in  the  cubic  sys- 
tem, page  4,  where  all  three  axes  are  equal,  this  is  unnecessary. 

However,  in  the  monoclinic  and  triclinic  systems,  where  either  one 
or  more  axes  intersect  obliquely,  it  is  not  only  necessary  to  give  the  axial 
ratio  but  also  to  indicate  the  values  of  the  angles  between  the  crystallo- 
graphic  axes.  For  example,  gypsum  (CaSO4.2H2O)  crystallizes  in  the 
monoclinic  system  and  has  the  following  axial  ratio : 

a  :  b  :  c  =  0.6896  :  1  :  0.4133 

and  the  inclination  of  the  a  axis  to  the  c  is  98°  58'.     This  angle  is  known 
as  /3,  Fig.  30. 

In  the  triclinic  system,  since  all  axes  are  inclined  to  each  other,  it  is 
also  necessary  to  know  the  value  of  the  three  angles,  which  are  located 
as  shown  in  Fig.  31,  viz. :  6  A  c  =  a,  a  Ac  =  0,  a  A  b  =  y. 


i-c 


-b- 


-a 


-c 
FIG.  30. 


Elements  of  Crystallization. — The  axial  ratio  and  the  angles  show- 
ing the  inclination  of  the  axes  are  termed  the  elements  of  crystallization. 
Thus,  the  triclinic  mineral  albite  (NaAlSi3O8)  possesses  the  following 
elements  crystallization : 

a  :  b  :  c  =  0.6330  :  1  : 0.5573. 
a  =      94°    5' 
0  =  116°  27' 

y  =      88°    7' 

If  the  angles  between  the  crystallographic  axes  equal  90°,  they  are  not 
indicated.  Therefore,  in  the  tetragonal,  hexagonal,  and  orthorhombic 
systems,  the  axial  ratios  alone  constitute  the  elements  of  crystallization, 
while  in  the  cubic  system,  there  are  no  unknown  elements. 

Rationality  of  Coefficients. — The  parametral  ratio  of  any  face  may 
be  expressed  in  general  by  na  :  pb  :  me,  where  the  coefficients  n}  p,  m, 
are  according  to  observation  always  rational.  In  Fig.  32,  the  inner 
bipyramid  is  assumed  to  be  the  fundamental  form,  page  5,  with  the 
following  value  of  the  intercepts:  oa  =  1.256,  ob  =  1,  oc  =  0.752. 


8 


MINERALOGY 


Being  a  fundamental  or  unit  form,  the  coefficients  n,  p,  m,  are  obviously 
all  equal  to  unity.     The  ratio  is,  hence,  a  :  b  :  c. 


The 


FIG.  32. 

outer  bipyramid,  however,  possesses  the  intercepts,  oa  =  1.256, 

oB  =  2,  oC  =  2.256.  These  lengths, 
divided  by  the  unit  lengths  of  each  axis, 
as  indicated  above,  determine  the 
values  of  n,  p,  and  m  for  the  outer  bi- 
pyramid, namely: 

1.256  2 


n  = 


1.256 


m  = 


=  1; 

2.256 
0.752 


2; 


=  3. 


FIG.  33.— Rene  Hauy  (1743-1822). 
Curator  of  mineralogy  in  the  Museum 
of  Natural  History  of  Paris  (1802- 
1822).  Pioneer  crystallographer  and 
discoverer  of  many  laws  of  crystallo- 
graphy, including  that  of  the  ration- 
ality of  coefficients. 

But  since,  in  this  case,  n  =  1 

a 


These  values  of  n,  p}  and  m,  are, 
therefore,  rational.  Such  values  as  J^, 
^i)  M?  %i  or  %  are  also  possible,  but 
never  3.1416  +,  2.6578  +,  \/3,  and  so 
forth. 

Symbols. — The  parametral  ratio  of 
the  plane  ABM,  Fig,  25,  may  be  writ- 
ten as  follows : 

na  :  pb  :  me. 

,  p  =  1,  m  =  3,  the  ratio  becomes: 
: b  :  3c. 


CRYSTALLOGRAPHY 


If,  however,  the  coefficients  had  the  values  J^, 
the  ratio  would  then  read: 


,  and  ^.  respectively, 


This,  when  expressed  in  terms  of  b,  becomes: 

%a  :  6  :  2c. 
Hence,  the  ratio 

na  :  b  :  me 

expresses  the  most  general  ratio  or  symbol  for  forms  belonging  to  the 
orthorhombic,  monoclinic,  and  triclinic  systems.  In  the  hexagonal 
and  tetragonal  systems,  since  the  a  and  b  axes  are  equal,  this  general 
symbol  becomes, 


Figure  34  shows  a  form,  the  ditetragonal  bipyramid,  with  the  symbol 
<z:2a:%e.  In  the  cubic  system,  all  three  axes  are  equal  and  the  general 
symbol  reads, 

a  :  na  :  ma. 

The  ratio  a :  oo  a  :  <»  a,  for  example,  symbolizes  a  form  in  the  cubic 
system  consisting  of  six1  faces,  which  cut  one  axis  and  extend  parallel  to 


FIG.  35. 


FIG.  36. 


the  other  two.  Such  a  form  is  the  cube,  Figs.  35  and  36.  The  ratio  a: 
2a  :  oo  a  represents  a  form  with  twenty-four  faces;  each  face  cuts  one  axis 
at  a  unit's  distance,  the  second  at  twice  the  distance,  but  extends  parallel 
to  the  third  axis.  Figures  37  and  38  shows  such  a  form,  the  tetrahexahe- 


10 


MINERALOGY 


dron.  This  system  of  crystallographic  notation  is  known  as  the  Weiss 
system.  These  symbols  are  most  readily  understood,  and  well  adapted 
for  beginners. 


FIG.  37. 


FIG.  38. 


Miller's  Indices. — In  this  system  of  notation  the  letters  referring  to 
the  various  crystallographic  axes  are  not  indicated,  the  values  given 
being  understood  as  referring  to  the  a,  6,  and  c  axes  respectively,  page  3. 

The  reciprocals  of  the  Weiss  parameters  are  re- 
duced to  the  lowest  common  denominator. 
The  numerators  then  constitute  the  Miller  sym- 
bols, called  ndices.  For  example,  the  recipro- 
cals of  the  Weiss  parameters  2a  :  b  :  3c  would 
be  J/£,  J4,  J^.  These,  reduced  to  the  lowest 
common  denominator,  are  %,  %,  %.  Hence, 
362  constitute  the  corresponding  Miller  indices. 
These  are  read  three,  six,  two. 

A  number  of  examples  will  make  this  system 
of  notation  clear.     Thus,  a  :  °°6  :  <&c,  becomes 
100;  2a  :  b  :  5c,  5.10.2;  a  :  a  :  3c,  331;  a  :  v>a  :  2c, 
201,  and   so  forth.     The  Miller  indices  corres- 
ponding to  the  general  ratios  a  :  na  :  ma  and 
na  :  b  :  me  are  written  hkl.     The  Miller  indices 
are  important  because  of  their  almost  univer- 
sal application  in  crystallographic  investigations. 
Elements  of  Symmetry. — The  laws  of  symmetry  find  expression  upon 
a  crystal  in  the  distribution  of  similar  angles  and  faces.     The  presence, 
therefore,  of  planes,  axes,  or  a  center  of  symmetry — these  are  the  elements 
of  symmetry — is  of  great  importance  for  the  correct  classification  of  a 
crystal. 

Planes  of  Symmetry. — Any  plane,  which  passes  through  the  center 
of  a  crystal  and  divides  it  into  two  symmetrical  parts,  the  one-half  being 
the  mirror-image  of  the  other,  is  a  plane  of  symmetry.  Figure  40  shows 
a  crystal  of  gypsum  (CaSO4 ,2H2O)  with  its  one  plane  of  symmetry.  Every 
plane  of  symmetry  is  parallel  to  some  face,  which  is  either  present  or 
possible  upon  the  crystal, 


FIG.  39. — Willian  H. 
Miller  (1801-1880).  Pro- 
fessor of  Mineralogy  in  the 
University  of  Cambridge 
(1832-1870). 


CRYSTALLOGRAPHY 


11 


It  is  sometimes  convenient  to  designate  planes  of  symmetry  as  axial 
and  diagonal,  or  as  principal,  or  intermediate  planes.  Figure  41  illus- 
trates a  crystal  of  the  tetragonal  system  with  five  planes  of  symmetry. 


u 


FIG.  40. 


Plane  c  is  the  horizontal  axial  or  principal  plane.     The  vertical  planes 
are  the  vertical  axial  (a)  and  intermediate  planes  of  symmetry. 

Axes  of  Symmetry.  —  The  line,  about  which  a  crystal  may  be  revolved 
as  an  axis  so  that  after  a  definite  angular  revolution  the  crystal  assumes 
exactly  the  same  position  in  space  which  it  originally  had,  is  termed  an 
axis  of  symmetry.  Depending  upon  the  rotation 
necessary,  only  four  types  of  axes  of  symmetry 
are  from  the  standpoint  of  crystallography  possible. 

(a)  Those  axes,  about  which  the  original  posi- 
tion is  reassumed  after  a  revolution  of  60°,  are  said 
to  be  axes  of  hexagonal,  six-fold,  or  six-count1  sym- 
metry. Such  axes  may  be  indicated  by  the  symbol 
%  .  Figure  43  shows  such  an  axis. 

(6)  If  the  original  position  is  regained  after  the 
crystal  is  revolved  through  90°,  the  axis  is  termed 
a  tetragonal,  four-count,  or  four-fold  axis  of  sym- 
metry. These  axes  are  represented  by  •  ,  as  illus- 
trated in  Fig.  44. 

(c)  Axes  requiring  an  angular  revolution  of  120° 
are  trigonal,  three-fold,  or  three-count  axes  of  sym- 
metry and  may  be  symbolized  by  A.     Figure  45 
illustrates  this  type  of  axis. 

(d)  A  binary,  two-fold,  or  two-count  axis  necessitates  a    revolution 
through  180°.     These  are  indicated  by  •   in  Fig.  44. 


FIG.    42.  —  Victor 

Coldschmidt  (1853 ). 

Professor  of  mineralogy 
in  the  University  of 
Heidelberg.  Author  of 
numerous  contributions 
on  crystallography. 


Because  in  a  complete  revolution  of  360°  the  position  is  reassumed  six  times. 


12 


MINERALOGY 


Center  of   Symmetry. — That  point  within  a  crystal  through  which 
straight  lines  may  be  drawn,  so  that  on  either  side  of  and  at  the  same 


FIG.  43. 


FIG.  44. 


FIG.  4,5. 


distance  from  it,  similar  portions  of  the  crystal  (faces,  edges,  angles,  and 

so  forth)  are  encountered,  is  a  center  of  symmetry.  Figure  46  has  a  center 
of  symmetry — the  other  elements  of  symmetry  are 
lacking. 

Angular  Position  of  Faces. — Since  crystals  are  often- 
times misshapen  or  distorted,  page  2,  it  follows  that  the 
elements  of  symmetry  are  not  always  readily  recog- 
nized. The  angular  position  of  the  faces  in  respect  to 
these  elements  is  the  essential  feature,  and  not  their 

distance  or  relative  size.     Figure  47  shows  an  ideal  crystal  of  augite. 

Here,  the  presence  of  a  plane  of  symmetry,  an  axis,  and  a  center  of 


FIG.  46. 


FIG.  47. 


FIG.  48. 


symmetry  is  obvious.  Figure  48  shows  a  distorted  crystal  of  the  same 
mineral,  possessing  however  exactly  the  same  elements  of  symmetry, 
because  the  angular  position  of  the  faces  is  the  same  as  in  Fig.  47. 


CRYSTALLOGRAPHY  13 

Classes  of  Symmetry. — Depending  upon  the  elements  of  symmetry 
present,  crystals  may  be  divided  into  thirty-two  distinct  groups,  called 
classes  of  symmetry.1  Only  forms  which  belong  to  the  same  class  can 
occur  in  combination  with  each  other.  A  crystal  system,  however,  in- 
cludes all  those  classes  of  symmetry  which  can  be  referred  to  the  same 
type  of  crystallographic  axes,  page  4.  The  various  elements  of  sym- 
metry and,  wherever  possible,  an  important  representative  are  given 
for  each  of  the  thirty-two  classes  in  the  tabular  classification  on  page  372. 
Only  13  classes  will  be"  discussed  in  detail. 

1  Also  termed  classes  of  crystals. 


/ 


-a 


U 


CHAPTER  II 
CUBIC  SYSTEM1 

Crystallographic  Axes. — All  crystals  which  can  be  referred  to  three 
equal  and  perpendicular  axes  belong  to  cubic  system.     Figure  49  shows 
the  axial  cross.     One  axis  is  held  vertically,  a  second  extends  from  front 
to  rear,  and  the  third  from  right  to  left.     These  axes  are  all  interchange- 
able, each  being  designated  by  a.     Since  there 
are  no   unknown   elements  of  crystallization  in 
this  system   (page  7),  all  substances,  regardless 
of  their  chemical  composition,   crystallizing  in 
this  system  with  forms  having  the  same  para- 
metral  ratios  must  of  necessity  possess  the  same 
interfacial  angles. 

Classes   of   Symmetry. — The   cubic   system 
includes   five   groups   or   classes   of   symmetry. 
FIG.  49.  Beginning  with  the  class  of  highest  symmetry, 

they  are: 

(1)  Hexoctahedral  Class 

(2)  Hextetrahedral  Class 

(3)  Dyakisdodecahedral  Class 

(4)  Pentagonal  icositetrahedral  Class 

(5)  Tetrahedral  pentagonal  dodecahedral  Class 

Of  these  classes,  the  first  three  are  the  most  important,  and  will  be  con- 
sidered in  detail. 

HEXOCTAHEDRAL  CLASS2 

Elements  of  Symmetry,  (a)  Planes. — Forms  of  this  class  are  char- 
acterized by  nine  planes  of  symmetry.  Three  of  these  are  parallel  to 
the  planes  of  the  Crystallographic  axes  and,  hence,  perpendicular  to  each 
other.  They  are  the  axial  planes  of  symmetry.  They  divide  space  into 
eight  equal  parts  called  octants.  The  six  other  planes  are  each  parallel  to 
one  of  the  Crystallographic  axes  and  bisect  the  angles  between  the  other 
two.  These  are  termed  the  diagonal  planes  of  symmetry.  By  them 
space  is  divided  into  twenty-four  equal  parts.  The  nine  planes  together 
divide  space  into  forty-eight  equal  sections.  Figures  50  and  51  illustrate 
the  location  of  the  axial  and  diagonal  planes,  respectively. 

(b)  Axes. — The  intersection  lines  of  the  three  axial  planes  of  symme- 
try give  rise  to  the  three  tetragonal  axes  of  symmetry.  These  are  the 

1  Also  termed  the  regular,  isometric,  tesseral,  or  tessular  system. 

2  Termed  by  Dana  the  normal  group. 

14 


CUBIC  SYSTEM 


15 


crystallographic  axes,  as  illustrated  by  Fig.  52.     The  four  axes  equally 
inclined  to  the  crystallographic  axes  are  of  trigonal  symmetry,  as  shown  by 


-1  —  ^,^1  —  -^ 

^ 

1 

1       i 

1 

1 

1 

! 

•l  — 

._Jr.-^:.ir._ 

-^ 

1 

i 

!     i 

1 

i     i 

1 

1 

i 

J  — 

--U-J- 

_ 

—  -z> 

FIG.  50. 


FIG.  51. 


Fig.  53.     There  are  also  six  axes  of  Unary  symmetry.     These  lie  in  the 
axial  planes  of  symmetry  and  bisect  the  angles  between  the  crystallo- 


T  '      JA^r-' 


^^ 

^^ 

^<i                    7^ 

^^ 

V^        \                7 

X  ^    \            ./. 

/ 

N  \    /  ./• 

x;x 
//  "N 

!/X  y7    \X\ 

Uc>4      \ 

-  ~~^ 

^/J-         _  ^,. 

^>^ 

FIG.  52. 


FIG.  53. 


FIG.  54. 


graphic  axes.     Their  location  is  indicated  in  Fig.  54.     These  thirteen 
axes  of  symmetry  may  be  indicated  as  follows: 


FIG.  55. 

/ 

(c)  Center. — The  forms  of  this  class  also  possess  this  element  of  sym- 
metiy.  Hence,  all  planes  have  parallel  counter-planes. 

The  projection  of  the  most  general  form  of  this  class  upon  a  plane  per- 
pendicular to  the  vertical  axis,  i.e,  in  this  case  an  axial  plane  of  symmetry, 
shows  the  symmetry  relations,1  Fig.  55. 

1  The  heavy  lines  indicate  edges  through  which  axial  planes  of  symmetry  pass. 
The  light,  full  lines  show  the  location  of  the  diagonal  planes,  while  dashed  lines  would 
indicate  the  absence  of  planes. 


16 


MINERALOGY 


Octahedron. — As  the  name  implies,  this  form  consists  of  eight  faces. 
Each  face  is  equally  inclined  to  the  crystallographic  axes.  Hence,  the 
parametral  ratio  may  be  written  (a  :  a  :  a),  which  according  to  Miller  would 
be  {111}.  The  faces  intersect  at  an  angle  of  109°  28'  16"  and  in  the 
ideal  form,  Figs.  56  and  57,  are  equal,  equilateral  triangles. 


FIG.  56. 


FIG.  57. 


The  crystallographic  axes  and,  hence,  the  axes  of  tetragonal  symmetry 
pass  through  the  tetrahedral  angles.  The  four  trigonal  axes  join  the 
centers  of  opposite  faces,  while  the  six  binary  axes  bisect  the  twelve 
edges. 

Dodecahedron. — This  form  consists  of  twelve  faces,  each  cutting  two  of 
the  crystallographic  axes  at  the  same  distance,  but  extending  parallel 
to  the  third.  The  symbols  are,  therefore,  (a:  a  :  oo  a),  or  {110}.  In  the 
ideal  form,  Figs.  58  and  59,  each  face  is  a  rhombus  and,  hence,  the  form 
is  often  termed  the  rhombic  dodecahedron. 


FIG.  58. 


FIG.  59. 


The  crystallographic  axes  pass  through  the  tetrahedral  angles,  the 
trigonal  axes  join  opposite  trihedral  angles,  and  the  binary  axes  the  centers 
of  opposite  faces.  It  follows,  therefore,  that  the  faces  are  parallel  to  the 
diagonal  planes  of  symmetry. 

Hexahedron  or  Cube. — The  faces  of  this  form  cut  one  axis  and  are 
parallel  to  the  other  two.  This  is  expressed  by  (a  :  «>  a  :  oo  a),  { 100} .  Six 
such  faces  are  possible  and  when  the  development  is  ideal,  Figs.  60  and 
61,  each  is  a  square. 

The    crystallographic   axes    pass  through  the  centers  of  the  faces. 


CUBIC  SYSTEM 


17 


The  trigonal  axes  of  symmetry  join  opposite  trihedral  angles,  while  the 
binary  axes  bisect  the  twelve  edges.     Compare  Figs.  52,  53  and  54. 


FIG.  60. 


FIG.  61. 


Trigonal  Trisoctahedron.1 — The  faces  of  this  form  cut  two  crystal- 
lographic  axes  at  equal  distances,  the  third  at  a  greater  distance,  ma. 
The  coefficient  ra  is  some  rational  value  greater  than  one  but  less  than 
infinity.  The  ratio  is  (a  :  a  :  ma)  and  it  requires  twenty-four  such  faces 
to  enclose  space.  The  Miller  symbols  are  {hhl},  where  h  is  greater  than 
I.  Because  the  general  outline  of  this  form  is  similar  to  that  of  the 
octahedron,  each  face  of  which  in  the  ideal  forms  is  replaced  by  three 
equal  isosceles  triangles,  it  is  termed  the  trigonal  trisoctahedron,  Figs. 
62  and  63,  (a  :  a  :  2a),  {221},  and  64,  (a  :  a  :  3a),  {331 J. 


FIG.  62. 


FIG.  63. 


FIG.  64. 


The  crystallographic  axes  join  opposite  octahedral  angles.  The 
trigonal  axes  pass  through  the  trihedral  angles  and  the  six  binary  axes 
bisect  the  twelve  long  edges. 

Tetragonal  Trisoctahedron.2 — This  form  consists  of  twenty-four  faces, 
each  cutting  one  axis  at  a  unit's  distance  and  the  other  two  at  greater 
but  equal  distances,  ma.  The  value  of  ra,  is,  as  above,  m  >  1  <  oo . 
The  symbols  are,  therefore,  (a  :ma  :md),  or  [hll] ,  h  >  I.  The  ideal 
forms,  Figs.  65  and  66,  (a  :  2a  :  2o),  {211},  and  67,  (a  :  4a  :4o),  {411}, 
bear  .some  resemblance  to  the  octahedron,  each  face  of  which  has  been 
replaced  by  three  four-sided  faces,  trapeziums,  of  equal  size.  The  form 
is,  therefore,  termed  the  tetragonal  trisoctahedron.  The  six  tetrahedral 
angles3  a  indicate  the  position  of  the  crystallographic  axes.  The 

1  Also  known  as  the  trisoctahedron. 

2  Also  termed  the  trapezohedron,  icositetrahedron,  and  leucitohedron. 

3  With  four  equal  edges. 

2 


18 


MINERALOGY 


trigonal  axes  of  symmetry  join  opposite  trihedral  angles,  while  those  of 
binary  symmetry  connect  the  tetrahedral  angles1  6. 


FIG.  65. 


FIG.  66. 


FIG.  67. 


Tetrahexahedron. — In  this  form  the  faces  cut  one  axis  at  a  unit's 
distance,  the  second  at  the  distance  ma,  where  m  >  1  <  oo ,  and  extend 
parallel  to  the  third  axis.  The  symbols  are,  therefore,  (a  :  ma  :  «>«),  or 
{hko} .  The  twenty-four  faces  in  the  ideal  forms,  Figs.  68  and  69, 
(a:  2a:  oca),  {210}, and  70,  (a:4a:  oo  a),  {4 10),  are  equal  isosceles  triangles. 
Since  this  form  may  be  considered  as  a  cube,  whose  faces  have  been  re- 
placed by  tetragonal  pyramids,  it  is  often  called  the  pyramid  cube  or 
tetrahexahedron. 


FIG.  68. 


FIG.  69. 


FIG.  70. 


The  crystallographic  axes  are  located  by  the  six  tetrahedral  angles. 
The  axes  of  trigonal  symmetry  pass  through  opposite  hexahedral  angles, 
while  the  binary  axes  bisect  the  long  edges. 

Hexoctahedron. — As  is  indicated  by  the  name,  this  form  is  bounded 
by  forty-eight  faces.  Each  cuts  one  crystallographic  axis  at  a  unit's 
distance,  the  other  two  at  greater  but  unequal  distances,  na  and  ma, 
respectively;  n  is  less  than  m,  the  value  of  m  being,  as  heretofore, 
m  >  I  <  oo.  Hence,  the  symbols  iriay  be  written  (a  :  na  :  ma),  or, 
{hkl}.  Figures  71  and  72  (a  :  3/2a  :  3d),  {321},  and  73,  (a  :  5/3a  :  5a) 
{531},  show  ideal  forms,  the  faces  being  scalene  triangles  of  the  same 
size. 


1  These  have  two  pairs  of  equal  edges. 


CUBIC  SYSTEM 


19 


The  crystallographic  axes  pass  through  the  octahedral  angles,  while 
the  hexahedral  angles  locate  those  of  trigonal  symmetry.  The  binary 
axes  pass  through  opposite  tetrahedral  angles. 

The  seven  forms  just  described  are  the  only  ones  possible  in  this  class. 


FIG.  71. 


FIG.  72. 


FIG.  73. 


Summary. — The    following    table    gives    a    summary  of   the    most 
important  features  of  the  hexoctahedral  class. 


Planes 

Axes 

fon-for 

Symmetry            A»al      !  Diaf5°nal 

•              A             • 

| 

1 

3                   6 

346 

1 

Forms 

Symbols 

oo 
• 

1 

Solid  angles 

1 

£_, 

Tetraliodral 

Hexaheclral 

Octahedral 

Weiss                 Miller 

i 

Octahedron 

a:  a:  a 

{111! 

8 

6 

- 

- 

Dodecahedron 

a:  a:  °°a 

{110! 

12 

8 

6 

- 

- 

Hexahedron 

ai  oo  o  '.  oo  a 

{100} 

6 

8 

-         - 

Trigonal  trisoctahedron 

a:  a:  ma 

[hhl\ 

24 

8 

— 

6 

Tetragonal  trisoctahedron 

a:  ma:  mo 

{hll} 

24 

8 

61  +  122 

- 

- 

Tetrahexahedron 

a  '.  ma  '.  oo  a 

{hko} 

24 

- 

6 

8 

- 

Hexoctahedron 

a:  na:  ma 

{hid} 

48 

- 

12 

8" 

6 

1  These  have  four  equal  edges. 

2  Two  pairs  of  two  equal  edges  each. 


20 


MINERALOGY 


From  this  tabulation  we  see  that  the  ratios  of  the  octahedron, 
dodecahedron,  and  hexahedron  contain  no  variables  and,  hence,  each 
is  represented  by  but  one  form.  These  are  often  called  singular  or 
fixed  forms.  The  other  ratios,  however,  contain  either  one  or  two 
variables  and,  therefore,  each  represents  a  series  of  forms.  Compare 
Figs.  62  to  73. 

Relationship  of  Forms. — The  relationship  existing  between  the  above 
forms  is  well  expressed  by  the  following  diagram: 

a  :  a  :  a 


a:  a:  ma     a  :  ma  :  ma 


a:na:  ma 


a:  a:  co  a 


a  :  oo  a  :  °°a 


The  three  fixed  forms  are  placed  at  the  corners  of  the  triangle  and, 
as  is  obvious,  must  be  considered  as  the  limiting  forms  of  the  others. 
For  example,  the  value  of  m  in  the  trigonal  trisoctahedron  (a  :  a  :  ma) 
varies  between  unity  and  infinity,  page  17.  Hence,  it  follows  that  the 
octahedron  and  dodecahedron  are  its  limiting  forms.  The  tetragonal 
trisoctahedron  (a  :  ma  :  ma)  similarly  passes  over  into  the  octahedron 
or  cube,  depending  upon  the  value  of  m.  The  limiting  forms  are,  there- 
fore, in  every  case  readily  recognized.  Those  forms,  which  are  on  the  sides 
of  the  triangle,1  lie  in  the  same  zone,  that  is,  their  intersection  lines  are 
parallel. 

Combinations. — The  following  figures  illustrate  some  of  the  com- 
binations of  the  forms,  which  are  observed  most  frequently. 


FIG.  74. 


Fio.  75. 


FIG.  76. 


Figures  74,  75,  and  76,  o  =  (a  :a  :a),  {m\;h=  (a:  c°a  :  »a),  {100}. 
This  combination  is  frequently  observed  on  galena  (PbS).  In  Fig. 
74,  the  octahedron  predominates,  in  Fig.  75  both  forms  are  equally 
developed,  while  in  Fig.  76  the  cube  is  the  predominant  form. 

Figure  77,  o  =  (a  :  a  :  a),  {lll};d  =  (a  :  a  :  o>0),  {110}.     Observed 
1  For  example,  the  octahedron,  trigonal  trisoctahedron,  and  dodecahedron. 


CUBIC  SYSTEM 


21 


on  spinel  (Mg (A1O2)  2) ,  magnetite  (Fe  (FeC^)  2) ,  and  f  ranklinite,  (Fe,ZuMn) 
(Fe02)2. 

Figure  78,  h  =  (a  :  <*>a  :  »&),  {100} ;  d  =  (a  :  a  :  ooa),  {HO}. 

Frequently  observed  on  galena  (PbS)  and  fluorite  (CaF2). 


FIG.  77. 


FIG.  78. 


FIG.  79. 


Figure  79,  d  =  (a  :a  :  op  a),  {110} ;  i  =  (a  :2a  :2a),  {211J.  This  is  a 
frequent  combination  on  garnet  (R3"R2'"Si4Oi2). 

Figures  80,  81,  and  82,  h  =  (a  :  coa  :  coa),  {100};  o  =  (a  :a  :a), 
fill'} ;  d  =  (a:a  :  °°  a)  { 110} .  Also  observed  on  galena  (PbS). 


FIG.  80. 


FIG.  81. 


FIG.  82. 


Figure  83,  h  =  (a  :  coa  :  coa),  {100} ;  e  =  (a  :  2a  :  coa),  {210}.  Ob- 
served on  copper  (Cu),  fluorite  (CaF2),  and  halite  (NaCl). 

Figure  84,  h  =  (a  :  coa  :  coa),  {100};  i  =  (a  :  2a  :  2a),  {211}.  Ob- 
served on  analcite  (NaAlSi206,  H2O)  and  argentite  (Ag2S). 


FIG.  83. 


FIG.  84. 


FIG.  85. 


Figure  85,  d  =  (a  :  a  :  »a),  {110};*  =  (a  :3/2a  :3a),  {321}. 
times  observed  on  garnet  (R3//R2///Si4Oi2). 


Some- 


22 


MINERALOGY 


HEXTETRAHEDRAL  CLASS1 

Elements  of  Symmetry. — The  elements  of  symmetry  of  this  class  con- 
sist of  six  diagonal  planes,  and  four  trigonal  and  three  binary  axes.  The 
trigonal  axes  are  polar  in  character.  The  crystallographic  axes  possess 
binary  symmetry.  The  diagonal  planes  of  symmetry  are  easily  located 
since  they  pass  through  the  edges  of  the  various  forms  of  this  class.  The 
symmetry  relations  are  shown  in  Fig.  86.  The  polarity  of  the  tri- 
gonal axes  and  absence  of  the  axial  planes  of 
symmetry  are  emphasized  by  the  shading  of  op- 
posite octants.  In  this  class,  there  are  four  new 
forms  which  differ  morphologically  from  those 
having  the  same  ratios  in  the  hexoctahedral  class, 
namely,  tetrahedrons,  tetragonal  tristetrahed- 
rons,  trigonal  tristetrahedrons,  and  hextetrahed- 
rons.  Of  these  forms  the  tetrahedrons  are  the 
most  important. 

Tetrahedrons. — These  are  bounded  by  four 
equilateral  triangles  intersecting  at  equal  angles 


FIG.   86. 


FIG.  87. 


FIG.  89. 


FIG.  90. 


of  70°  32'.     Each  face  is  equally  inclined  to  the  crystallographic  axes 
and  consequently  the  symbols  are  the  same  as  for  the  octahedron  (page 
16),    namely   ±  (a  :  a  :  a)    or  {ill}    and  {ill}      There  are  two  tetra- 
1  The  tetrahedral  group  of  Dana. 


CUBIC  SYSTEM 


23 


hedrons  possible  and  their  difference  depen.ds  upon  the  positions  they 
occupy  in  space,  as  illustrated  in  Figs.  87  to  90.  If  the  upper  face  to 
the  front  lies  in  the  positive  octant,  the  form  is  designated  as  positive 
(Figs.  88  and  90),  if  not,  it  is  negative  (Figs.  87  and  89).  The  forms 
are  said  to  be  congruent,  for  a  positive  form  may  be  brought  into  the 
position  of  a  negative  by  rotating  through  an  angle  of  90°  and  vice  versa. 

The  crystallographic  axes  pass  through  the  centers  of  the  edges  and 
possess  binary  symmetry.  The  trigonal  axes  pass  from  the  trihedral 
angles  to  the  centers  of  opposite  faces,  and  are  polar  in  character. 

Tetragonal  Tristetrahedrons. — These  forms  possess  a  tetrahedral 
habit  and  are  bounded  by  twelve  faces,  which  in  the  ideal  development 
are  similar  trapeziums.  Each  face  has  four  angles.  Plus  and  minus 
forms  are  possible.  The  symbols  are  the  same  as  for  the  trigonal  tris- 
octahedron,  page  17,  namely,  ±  (a  :  a  :  ma)  or  {hhl\  and  {hhl}.  The 
differentiation  between  positive  and  negative  forms  is  analogous  to  that 
referred  to  under  tetrahedrons.  Figure  92  represents  a  positive  form  and 
Fig.  91  a  negative.  These  forms  are  some  times  called  deltoids  or  deltoid 
dodecahedrons. 

The  crystallographic  axes  pass  through  opposite  tetrahedral  angles, 
while  the  axes  of  trigonal  symmetry  join  opposite  trihedral  angles, 
one  of  which  is  acute,  the  other  obtuse. 


FIG.  91. 


FIG.  92. 


Trigonal  Tristetrahedrons. — These  are  two  congruent  forms  bounded  by 
twelve  similar  isosceles  triangles,  Figs.  93  and  94.  The  habit  is  tetra- 
hedral, and  the  forms  might  be  considered  as  tetrahedrons  whose  faces 


FIG.  93. 


FIG.  94. 


24 


MINERALOGY 


have  been  replaced  by  trigonal  pyramids.  They  are  sometimes  called 
pyramid  tetrahedrons  or  trigonal  dodecahedrons.  The  symbols  are  analo- 
gous to  those  of  the  tetragonal  trisoctahedron,  page  17,  namely, 
±  (a:  ma:  ma)  or  {hll}  and  {hll}.  Figure  94  illustrates  the  positive 
position  and  Fig.  93  the  negative. 

The  crystallographic  axes  bisect  the  long  edges.  The  trigonal 
axes  pass  from  the  trihedral  angles  to  the  opposite  hexahedral. 

Hextetrahedrons. — When  these  forms  are  ideally  developed,  they 
possess  a  tetrahedral  habit  and  are  bounded  by  twenty-four  similar 
scalene  triangles.  They  are  congruent  and  hence  designated  as  positive, 
Fig.  96,  and  negative,  Fig.  95.  The  symbols  are  of  the  same  character 
as  those  of  the  hexoctahedron,  page  18,  namely,  ±  (a  ;  na  :  ma)  or  \hkl} 
and  {hkl\. 

The  crystallographic  axes  connect  opposite  tetrahedral  angles.  The 
trigonal  axes  of  symmetry  pass  through  opposite  hexahedral  angles,  one 
of  which  is  more  obtuse  than  the  other. 


FIG.  95. 


FIG.  96. 


Other  Forms. — The  hexahedron,  dodecahedron,  and  tetrahexahedron 
are  morphologically  exactly  similar  to  those  of  the  hexoctahedral  class. 
Their  symmetry  is  however  of  a  lower  grade.  This  is  not  recognized  on 
models.  On  crystals,  however,  the  luster,  surface  striations,  and  form 
and  position  of  etch  figures  reveal  the  lower  grade  of  symmetry.* 

*  When  crystals  are  subjected  to  the  action  of  some  solvent  for  a  short  time,  small 
depressions  or  elevations,  the  so-called  etch  figures,  appear.  Being  dependent  upon  the 
internal  molecular  structure,  their  form  and  position  indicate  the  symmetry  of  the 


FIG.  97. 


FIG.  98. 


crystal.  For  instance,  Fig.  97  shows  the  etch  figures  on  a  crystal  (cube)  of  halite, 
NaOl.  Here,  it  is  evident,  that  the  symmetry  of  the  figures  with  respect  to  that  of 
the  cube  is  such  as  to  place  the  crystal  in  the  hexoctahedral  class.  Figure  98  repre- 
sents a  cube  of  sylvite,  KC1,  which  geometrically  does  not  differ  from  the  crystal  of 
halite.  A  lower  grade  of  symmetry  is,  however,  revealed  by  the  position  of  the  etch 


CUBIC  SYSTEM 


25 


Naturally  when  these  forms  occur  in  combination  with  those  which 
are  morphologically  new,  the  lower  grade  of  symmetry  of  this  class  is  at 
once  apparent. 

Summary. — The  following  table  shows  the  important  features  of  the 
forms  of  this  class  of  symmetry. 


Planes                                          Axes 

|                                                                                                                             ; 

Center 

Axial 
Symmetry 

Diagonal 

• 

A 

• 

0 

A 

0 

4 

3 

0 

(Polar) 

Solid    angles 


oymoois 

Faces 

- 

•5 

1 

Weiss                      Miller 

1 

Tetrah 

c 

W 

Tetrahedrons                                              +  a:  a:  a 
(111  | 

>' 

4 

— 

— 

Tetragonal  tristetrahedrons                    ±  a:  a:  ma           {1,17! 

}- 

4+4 

6 

— 

Trigonal  tristetrahedrons                         ±  a:  ma:  ma  \       \hjj\ 

}» 

4* 

— 

4 

Hextetrahedrons                                        ±  a  :  na  :  ma         !  j,  £  /  1 

>- 

— 

6 

4 

+ 
4 

Dodecahedron 

a',  a'.  °°  a 

{110} 

1 

Morphologically 

Tetrahexahedron 

a  '.  ma  '.  °°  a 

\hko] 

the  same  as  in  the 
hex  octahedral 

Hexahedron 

a'.  c»ai  oo  a 

{100} 

class. 

figures.  This  crystal  belongs  to  the  pentagonal  icositetrahedral  class,  page  14,  for 
no  planes  of  symmetry  can  be  passed  through  these  figures,  which  at  the  same  time  are 
planes  of  symmetry  of  the  cube,  as  is  the  case  with  the  crystal  of  halite. 


FIG.  100. 


FIG.   101. 


FIG.  99. 

Figures  99,  100,  and  101  show  three  cubes  representing  crystals  of  fluorite,  CaF2 
(Fig.  99),  sphalerite,  ZnS  (Fig.  100),  and  pyrite,  FeS2  (Fig.  101).     From  the  char- 


26 


MINERALOGY 


Combinations. — Some  of  the  more  common  combinations  are  illus- 
trated by  the  following  figures: 


FIG.  102. 


FIG.  103. 


FIG.  104. 


Figure  102,  o  =  (a:a:a),  (111);*/  =-(a:a:a),  {ill}.  This  combina- 
tion is  common  on  sphalerite  (ZnS). 

Figure  103,  h  =,(a:*>a:<x>a),  {I00};o  =  (a:a:a),  {ill}.  Observed  on 
sphalerite  (ZnS)  and  tetrahedrite  (Cu2,  Fe,  Zn)4(As,  Sb)2S7. 

Figure  104,  o  -  (a:a:a),  {III} ;  h  =  (a:«>a:<x>a),  {100}.  Observed 
on  boracite  (Mg7Cl2Ci6O3o)  and  tetrahedrite  (Cu2,Fe,Zn)4(As,Sb)2S7. 


FIG.  105. 


FIG.  106. 


FIG. 


Figures  105,  106,  and  107,  o  =  (a:a:a),  {ill};  i  =  (a:2a:2a),  {211}; 
d  =  (a:a:°°a).  {110}.     Frequent  on  tetrahedrite  (Cu2,  Fe,Zn)4  (As,  Sb)2S7. 


DYAKISDODECAHEDRAL  CLASS 

Elements  of  Symmetry. — The  elements  of 
symmetry  of  this  class  consist  of  three  axial 
planes,  three  binary  and  four  trigonal  axes,  and 
the  center  of  symmetry.  The  crystallographic 
axes  possess  binary  symmetry.  Figure  108 
shows  the  symmetry  relations. 

There  are  two  new  forms  in  this  class  which 
differ  morphologically  from  those  thus  far  con- 
sidered, namely,  the  pyritohedrons  and  dyakis- 
dodecahedrons. 


FIG.   108. 


acter  and  position  of  the  striations  on  the  faces  of  these  cubes,  it  is  at  once  recognized 
that  through  Fig.  99.  nine  planes  of  symmetry  may  be  passed,  through  Fig.  100 
six,  and  through  Fig.  101  only  three.  That  is,  the  striations  indicate  clearly  that 
fluorite  has  the  symmetry  of  the  hexoctahedral  class,  sphalerite  of  the  hextetrahedral 
class,  and  pyrite  of  the  dyakisdodecahedral  class. 


CUBIC  SYSTEM 


27 


Pyritohedrons. — The  symbols  of  these  forms  are  analogous  to  those 
of  the  tetrahexahedron,  page  18,  namely,  ±(a  :  ma  :  «>  a)  or  {hko}  and 
{kho\.  There  are  two  congruent  forms  possible,  Fig.  110,  positive,  and 
Fig.  109,  negative. 

Each  form  is  bounded  by  twelve  similar  faces.  The  faces  are  un- 
equilateral  pentagons,  four  sides  of  which  are  equal.  The  crystallographic 
axes  possess  binary  symmetry  and  bisects  the  six  long  edges.  The  trig- 
onal axes  pass  through  the  trihedral  angles,  the  edges  of  which  are  of 
equal  lengths.  The  three  planes  of  symmetry  pass  through  the  long 


FIG.  109. 


FIG.  110. 


edges.  These  forms, are  termed  pyritohedrons  because  they  are  very 
frequently  observed  upon  the  very  common  mineral  pyrite,  FeS2.  They 
are  also  designated  as  pentagonal  dodecahedrons.1 

Dyakisdodecahedrons. — These  are  congruent  forms  bounded  by 
twenty-four  similar  trapeziums  and  possess  symbols  corresponding  to 
the  hexoctahedron,  namely,  ±(a  :na  :  ma)  or  {hkl}  and  {hlk}.  They 
are  some  times  termed  didodecahedrons  or  diploids.  Figure  112  shows  a 
positive  form  and  Fig.  Ill  a  negative.  The  crystallographic  axes  pass 


FIG.  111. 


FIG.  112. 


through  the  six  tetrahedral  angles  possessing  two  pairs  of  equal  edges. 
The  trigonal  axes  join  opposite  trihedral  angles.  The  three  planes  of 
symmetry  pass  through  the  continuous  edges. 

1  The  regular  pentagonal  dodecahedron  of  geometry,  bounded  by  equilateral  pen- 
tagons intersecting  in  equal  edges  and  angles  is  crystallographically  an  impossible 


form,  the  value  of  m  being 


1  +  V5 


which  is  irrational. 


28 


MINERALOGY 


Other  Forms:  The  hexahedron,  octahedron,  dodecahedron,  trigonal 
trisoctahedron,  and  tetragonal  trisoctahedron  occur  in  this  class  with  the 
same  morphological  development  as  in  the  hexoctahedral  class.  They, 
however,  possess  a  lower  grade  of  symmetry.  If  they  occur  independ- 
ently, the  lower  grade  of  symmetry  may  be  recognized  by  etch  figures  or 
peculiar  physical  characteristics  of  the  faces.  (See  page  24.) 

Summary. — In  the  following  table,  the  important  features  of  the 
various  forms  of  this  class  are  given. 


Symmetry 

Planes 

Axes 

Center 

Axial 

Diagonal 

• 

A 

• 

3 

0 

0 

4 

3 

1 

Forms 

Symbols 

Faces 

Solid  angles 

Trihedral 

Tetrahe- 
dral 

*CS    CQ 

3  o> 

•» 

1-1  »a 

«N§ 

<N  <n 

NW 

+  a> 

-1 

+H 

<N 

Weiss 

Miller 

Pyritohedrons 

+  a'.ma'.  °°a 

{hko} 
{kho} 

}, 

8 

12 

— 

— 

Dyakisdodecahedrons 

+  a:  na:  ma 

{hkl} 
{hlk\ 

}- 

8 

- 

6 

12 

Octahedron 

a:  a:  a 

{111} 

Morphologically  the  same  as 
in  the  hexoctahedral  class. 

Dodecahedron 

a:  a:  ^a 

{110} 

Hexahedron 

a:  coa:  ooa 

{100} 

Trigonal  trisoctahedron 

a:  a:  ma 

{hhl} 

Tetragonal    trisoctahe- 
dron 

a:  ma:  ma 

{hll} 

CUBIC  SYSTEM 


29 


Combinations. — The    accompanying    figures    show    some    combina- 
tions of  the  forms  of  this  class. 


FIG.  113. 


FIG.   116. 


FIG.  11' 


FIG.  118. 


Figures  113  to  118,  o  =  (a  :  a  :  a),  {111}  -,  e  =  (a  :ma  :  coa),  {210}; 
fc  =  (a  :  »a:  »a),  {100};n  =  (a:%a:3o),  {321}.  These  combinations 
are  frequently  observed  on  pyrite,  FeS2. 


CHAPTER  III 


+c 


HEXAGONAL  SYSTEM 

Crystallographic  Axes.— This  system  includes  all  crystals  which  can 
be  referred  to  four  axes,  three  of  which  are  equal  and  lie  in  an  horizontal 
plane,  and  intersect  each  other  at  an  angle  of  60°.  These  are  termed  the 
lateral  axes,  being  designated  by  the  letter  a.  These  axes  are  interchange- 
able. The  fourth,  or  principal  axis  is  perpendicular  to  the  plane  of  the 
lateral  axes  and  is  termed  the  c  axis.  It  may  be  longer  or  shorter  than 
the  lateral  axes.  The  three  equal  axes,  which  bisect  the  angles  between 
the  lateral  axes,  are  the  intermediate  axes.  These  may  be  designated  by 

6.     Figure  119  shows  an  axial  cross  of  this 
system. 

In  reading  crystals  of  the  hexagonal  sys- 
tem, it  is  customary  to  hold  the  c  axis  verti- 
cally, letting  one  of  the  lateral  or  a  axes  extend 
from  right  to  left.  The  extremities  of  the 
lateral  axes  are  alternately  characterized  as 
plus  and  minus,  see  Fig.  119.  In  referring 
a  form  to  the  crystallographic  axes,  it  is 
common  practice  to  consider  them  in  the 
following  order;  ai  first,  then  a2,  thirdly  aS) 
-c  and  lastly  the  c  axis.  The  symbols  always 

FlG-  119-  refer  to  them  in  this  order.     It  is  also  to  be 

noted  that  in  following  this   order,    one   of 
the  lateral  axes  will  always  be  preceded  by  a  minus  sign. 

Since  the  lengths  of  the  a  and  c  axes  differ,  it  is  necessary  to  assume 
for  each  substance  crystallizing  in  this  system  a  fundamental  form,  whose 
intercepts  are  taken  as  representing  the  unit  lengths  of  the  lateral  and 
principal  axes,  respectively.  The  ratio,  which  exists  between  the  lengths 
of  these  axes  is  called  the  axial  ratio  and  is  always  an  irrational  value, 
the  a  axis  being  assumed  as  unity,  page  6. 

Classes  of  Symmetry. — The  hexagonal  system  includes  a  larger  num- 
ber of  classes  of  symmetry  than  any  other  system,  namely,  twelve.  Be- 
ginning with  the  class  of  highest  symmetry,  they  are : 

*  1.  Dihexagonal  bipyramidal  class 

*  2.  Dihexagonal  pyramidal  class 
t     3.  Ditrigonal  bipyramidal  class 


{*  4.  Ditrigonal  scalenohedral  class 


30 


HEXAGONAL  SYSTEM 


31 


*  5.  Hexagonal  bipyramidal  class 

6.  Hexagonal  trapezohedral  class 
f*  7.  Ditrigonal  pyramidal  class 
8.  Hexagonal  pyramidal  class 
It  9.  Trigonal  bipyramidal  class 
|*10.  Trigonal  trapezohedral  class 
t*ll.  Trigonal  rhombohedral  class 
|  12.  Trigonal  pyramidal  class 

Those  classes  marked  with  an*  are  the  most  important,  for  nearly 
all  of  the  crystals  of  this  system  belong  to  some  one  of  them.  No  repre- 
sentative has  as  yet  been  observed  for  the  class  marked  by  f-  Those 
marked  {  are  often  grouped  together  and  form  the  trigonal  system. 
Only  classes  1,  4,  5,  7,  and  10  will  be  discussed  in  detail.  A  fairly  com- 
prehensive idea  of  the  hexagonal  system,  amply  sufficient  for  beginning 
students,  may  be  obtained  from  a  consideration  of  classes  1  and  4. 

DIHEXAGONAL  BIPYRAMIDAL  CLASS1 

Symmetry. — This  class  possesses  the  highest  grade  of  symmetry  of 
any  in  the  hexagonal  system. 


FIG.  120. 


FIG.  121. 


(a)  Planes. — In  all  there  are  seven  planes  of  symmetry.  One  of  these, 
the  horizonal  axial  or  principal  plane,  is  the  plane  of  the  horizontal  axes. 
The  other  planes  are  vertical  and  are  divided  into  two  series  of  three 
each,  which  are  termed  the  vertical  axial  and  the  intermediate,  respec- 
tively. They  intersect  at  angles  of  60°.  The  intermediate  planes  bisect 
the  angles  between  the  vertical  axial. 

The  four  axial  planes  divide  space  into  twelve  equal  parts,  called 
dodecants;  the  seven  planes,  however,  into  twenty-four  parts,  Mg.  120. 

These  planes  are  often  designated  as  follows: 

1  Horizontal  Axial  +  3  Vertical  Axial  +  3  Vertical  Intermediate  = 

7  Planes. 

1  The  normal  group  of  Dana. 


32  MINERALOGY 

(b)  Axes. — The  c  axis  is  an  axis  of  hexagonal  symmetry,  while  the 
lateral  and  intermediate  axes  possess  binary  symmetry.     These  axes  are 
often  indicated,  thus, 

1  •  +  3  •   +  3  •    =  7  axes. 

(c)  Center. — This  element  of  symmetry  is  also  present,  requiring  every 
face  to  have  a  parallel  counter-face.     Figure  121,  the  projection  of  the 
most  complicated  form  upon  a  plane  perpendicular  to  the  vertical  axis, 
shows  the  elements  of  symmetry  of  this  class. 

Hexagonal  Bipyramid  of  the  First  Order. — From  Fig.  122,  it  is 
obvious  that  any  plane  which  cuts  any  two  adjacent  lateral  axes  at  the 
unit  distance  from  the  center  must  extend  parallel  to  the  third.  If  such 
a  plane  be  assumed  to  cut  the  c  axis  at  its  unit  length  from  the  center, 
the  parametral  ratio  would  then  be 

a3 :  c. 


FIG.  122.  FIG.  123. 

According  to  the  above  elements  of  symmetry,  twelve  planes  possess- 
ing this  ratio  are  possible.  They  enclose  space  and  give  rise  to  the  form 
termed  the  hexagonal  bipyramid1  of  the  first  order,  Figs.  122  and  123.  In 
the  ideal  form,  the  faces  are  all  equal,  isosceles  triangles.  The  symbols 
are  (a  :<»a  :  a  :  c),  {lOll}.2  Because  the  intercepts  along  the  c  and  two 
lateral  axes  are  taken  as  units,  such  bipyramids  are  also  known  as  fun- 
damental or  unit  bipyramids,  page  5. 

Planes  are,  however,  possible  which  cat  the  two  lateral  axes  at  the 
unit  distances,  but  intercept  the  c  axis  at  the  distance  me,  the  coefficient 
m  being  some  rational  value  smaller  or  greater  than  1,  see  page  7.  Such 
bipyramids,  according  as  m  is  greater  or  less  than  unity,  are  more  acute 
or  obtuse  than  the  fundamental  form.  They  are  termed  modified 
hexagonal  bipyramids  of  the  first  order.  Their  symbols  are 

(a  :  oo  a  :  a  :  me)  or  { hohl } ,  where  m  =  -,,  also  m  >  0  <  oo . 

1  Since  these  are  really  double  pyramids,  the  term  bipyramid  is  employed. 

2  In  this  system  it  is  advantageous  to  employ  the  indices  as  modified  by  Bravaia 
(hikl)  rather  than  those  of  Miller,  who  uses  but  three. 


HEXAGONAL  SYSTEM 


33 


The  principal  axis  passes  through  the  hexahedral  angles,  the  lateral 
axes  join  tetrahedral  angles,  while  the  intermediate  bisect  the  horizontal 
edges.  Hence,  when  such  bipyramids  are  held  correctly,  a  face  is  directed 
towards  the  observer.  The  various  axes  of  symmetry  are  located  by 
means  of  the  above. 

Hexagonal  Bipyramid  of  the  Second  Order. — In  form,  this  bipyramid 
is  similar  to  the  preceding.  It  is,  however,  to  be  distinguished  by  its 


FIG.  125. 


position  in  respect  to  the  lateral  axes.  The  bipyramid  of  the  second 
order  is  so  held  that  an  edge,  and  not  a  face,  is  directed  towards  the 
observer.  This  means  that  the  lateral  axes  are  perpendicular  to  and 
bisect  the  horizontal  edges  as  shown  in  Figs.  124  and  125.  Figure  126 
shows  the  cross-section  including  the  secondary  axes.  From  these  figures 


FIG.  126. 


it  is  obvious  that  each  face  cuts  one  of  the  lateral  axes  at  a  unit  distance, 
the  other  two  at  greater  but  equal  distances.  For  example,  AB  cuts 
a  3  at  the  unit  distance  OS,  and  ai  and  a2  at  greater  but  equal  distances 
OM  and  ON,  respectively. 


34  MINERALOGY 

The  following  considerations  will  determine  the  length  of  OM  and 
ON,  the  intercepts  on  ai  and  a2,  in  terms  of  OS  =  1. 

As  already  indicated,  the  lateral  axes  are  perpendicular  to  the  hori- 
zontal edges,  hence  OS  and  ON  are  perpendicular  to  AB  and  BC, 
respectively.  Therefore,  in  the  right  triangles  ORB  and  NRB,  the 
side  RB  is  common  and  the  angles  OBR  and  NBR  are  equal.1 

Therefore,  OR  =  RN.     But  OR=  OS  =  1. 

Hence,  ON  =  OR  +  RN=  2. 

In  the  same  manner  it  can  be  shown  that  the  intercept  on  «i  is 
equal  to  that  along  a2,  that  is,  twice  the  unit  length.  The  parametral 
ratio  of  the  hexagonal  bipyramid  of  the  second  order,  therefore,  is 

rtjL 

(2a  :  2a  :  a  :  me),  or    {hh2hl},  where  -r-  =  m.     Fig.      126      shows     the 

positions  of  the  bipyramids  of  both  orders  with  respect  to  the  lateral 
axes,  the  inner  outline  representing  that  of  first,  the  outer  the  one  of 
of  the  second  order.  , 

Dihexagonal  Bipyramid. — The  faces  of  this  form  cut  the  three  lateral 
axes  at  unequal  distances.  For  example,  in  Fig.  127  the  face  repre- 
sented by  dB  cuts  the  0,1  axis  at  A,  a2  at  C,  and  a3  at  B.  Assuming  the 
shortest  of  these  intercepts  as  unity,  hence,  OB  =  a=  1,  we  at  once 


see  that  one  of  these  axes  is  cut  at  a  unit's  distance  from  0,  the  other 
two,  however,  at  greater  distances.  If  we  let  the  intercepts  OA  and 
OC  be  represented  by  n(OB)  =  na,  and  p(OB)  =  pa,  respectively, 
the  ratio  will  read 

(na  :pa  :  a  :  me,)  {hikl}. 

n 
In    this    ratio    p  =  — — r-     Twenty-four  planes  having  this  ratio 

1  Since  angle  ABC  equals  120°,  angle  NBR  is  60°,  being  the  supplement  of  ABC. 
But  the  intermediate  axis  OZ  bisects  the  angle  ABC,  hence  angle  OBR  is  also  60°. 


HEXAGONAL  SYSTEM 


35 


are  possible  and  give  rise  to  the  form  called  the  dihexagonal  bipyramid, 
Figs.  128  and  129.  In  the  ideal  form  the  faces  are  equal,  scalene  triangles 
cutting  in  twenty-four  polar1),  a  and  b,  and  twelve  equal  basal2)  edges. 
The  polar  edges  and  angles  are  alternately  equal.  This  is  shown  by 
Fig.  130,  where  the  heavy  inner  outline  represents  the  form  of  the  first 


FIG.  128. 


FIG.   129. 


order,  the  outer  the  one  of  the  second,  and  the  intermediate  outlines 
the  dihexagonal  type  in  respect  to  the  lateral  axes. 

These  three  hexagonal  bipyramids  are  closely  related,  for,  if  we 
suppose  the  plane  represented  by  A  B,  Fig.  130  to  be  rotated  about 
the  point  B  so  that  the  intercept  along  «2  increases  in  length,  the  one 


FIG.   130. 

along  «i  decreases  until  it  equals  oB'  =  oB  =  1.  Then  the  plane  is 
parallel  to  a2  and  the  ratio  for  the  bipyramid  of  the  first  order  results. 
If,  however,  AB  is  rotated  so  that  the  intercept  along  a2  is  decreased 
in  length,  the  one  along  «i  increases  until  it  equals  oC  =  2oB'  =  2a. 
When  this  is  the  case,  the  intercept  on  a2  is  also  equal  to  2a,  for  then 

1  Those  joining  the  horizontal  and  principal  axes. 

2  These  lie  in  the  horizontal  plane  of  symmetry. 


36 


MINERALOGY 


the  plane  is  perpendicular  to  a3.  This  gives  rise  to  the  ratio  of  the 
bipyramid  of  the  second  order. 

That  the  bipyramids  of  the  first  and  second  orders  are  the  limiting 
forms  of  the  dihexagonal  bipyramid  is  also  shown  by  the  fact  that 

p  = =•     For,  if  n  =  1,  it  follows  that  p  =  <»,  hence,  the  ratio  of 

ft  ~~~  JL 

the  form  of  the  first  order.  But,  when  n  =  2,  p  =  2  also,  therefore,  the 
ratio  for  the  second  order  results.  With  dihexagonal  bipyramids  the 
following  holds  good; 

n  >  1  <  2,  and  p  >  2  <  o> . 

The  dihexagonal  bipyramid  whose  polar  edges  and  angles  are  all 
equal  is  crystallographically  not  a  possible  form,  because  the  value  of 
n  would  then  be  J^(l  +  A/3)  =  \/2  .  sin  75°  =  1. 36603 +,  which  of 
course  is  irrational.  It  also  follows  that  in  those  dihexagonal  bipyramids, 
where  the  value  of  n  is  less  than  1. 36603 +,  for  instance,  %  =  1.20, 
the  more  acute  pole  angles  indicate  the  location  of  the  lateral  axes,  the 
more  obtuse  that  of  the  intermediate,  and  vice  versa,  when  n  is  greater 
than  1.36603+  ,  for  example,  %  =  1.60.  This  is  clearly  shown  by 
Fig.  130. 


FIG.   131. 


FIG.   132. 


Hexagonal  Prism  of  the  First  Order. — This  form  is  easily  derived  from 
the  bipyramid  of  the  same  order  by  allowing  the  intercept  along  the  c  axis 
to  assume  its  maximum  value,  infinity.  Then  the  twelve  planes  of  the 
bipyramid  are  reduced  to  six,  each  plane  cutting  two  lateral  axes  at  the 
unit  distance  and  extending  parallel  to  the  c  axis.  The  symbols  are 
(a  :  oo  a  :  a  :  oo  c)  or  {1010}.  This  form  cannot  enclose  space  and,  hence, 
may  be  termed  an  open  form,  page  5.  It  cannot  occur  independently 
and  is  always  to  be  observed  in  combination,  Fig.  131.  The  lateral 
axes  join  opposite  edges,  i.e.,  a  face  is  directed  towards  the  observer  when 
properly  held. 

Hexagonal  Prism  of  the  Second  Order. — This  prism  bears  the  same  rela- 
tion to  the  preceding  form  that  the  bipyramid  of  the  second  order  does 
to  the  one  of  the  first,  page  33.  The  symbols  are  (2a  :  2a  :  a  :  oo  c)  or 
{1120}.  It  is,  hence,  an  open  form  consisting  of  six  faces.  The  lateral 
axes  join  the  centers  of  opposite  faces,  hence,  an  edge  is  directed  towards 
the  observer,  Fig.  132. 


HEXAGONAL  SYSTEM 


37 


.-.— • 


Dihexagonal  Prism. — This  form  may  be  obtained  from  the  correspond- 
ing bipyramid  by  increasing  the  value  of  m  to  infinity,  which  gives 
(na  :  pa  :  a  :  <»  c) ,  or  { hiko } .  This  prism  consists  of  twelve  faces  whose  alter- 
nate edges  and  angles  are  equal.  This  form,  Fig.  133,  is  closely  related 
to  the  corresponding  bypyramid  and,  hence,  all  that  has 
been  said  concerning  the  dihexagonal  bipyramid,  page  35, 
with  respect  to  the  location  of  the  lateral  axes  and  its 
limiting  forms  might  be  repeated  here,  substituting,  of 
course,  for  the  bipyramids  of  the  first  and  second  orders 
the  corresponding  prism. 

Hexagonal  Basal  Pinacoid. — The  faces  of  this  form 
are  parallel  to  the  horizontal  plane  of  symmetry  and  possess 
the  following  symbols  (°°a:  ^ai^a:  «>c),  |0001}.  It  is  evident  from 
the  presence  of  a  center  and  horizontal  axial  plane  of  symmetry  that 
two  such  planes  are  possible.  This,  like  the  prisms,  is  an  open  form  and 
must  always  occur  in  combination.  Figure  131  shows  this  form  in 
combination  with  the  prism  of  the  first  order. 

Summary. — The  seven  forms  of  this  class  and  their  principal  features 
mav  be  summarized  as  follows: 


FIG.   133. 


Symmetry 

Planes                                                Axes 

Center 

Horizontal 

Vertical 

Vertical 

Horizontal 

Axial 

Axial 

Intermediate 

^* 

Axial 

Axial 

Intermediate 

1  3 


ftymoo 

is 

s 

•3 

•Q 

IE 

Weiss 

Miller- 
Bra  vais 

Number 

Tetrahe 

Hexahec 

§« 

•v* 

Unit  Bipyramid  —  First  order  
Modified  Bipyramids  —  First  order. 
Bipyramids  —  Second  order  
Dihexagonal  Bipvramids;  

a:  oo  a:  a:  c 
a:  ooa:  a:  me 
2a:  2a:  a:  me 
na:  pa:  a:  me 

11011} 

{hohl} 
{hh2hl} 
{hikl} 

12 
12 
12 
?4 

6 
6 
6 
6+6 

1 

? 

Prism—  First  order  
Prism  —  Second  order 

a:  ma:  a:  °oc 

2a  °.  2o  :  a  :  °°  c 

{1010} 
{1120} 

6 
6 

Dihexagonal  Prisms 

na:  pa:  a:  °oc 

{hiko} 

12 

Basal  Pinacoid  

°oa:  ooa:  ooa:  c 

{0001} 

2 

Solid  angles 


38 


MINERALOGY 


Relationship  of  Forms.  —  The  following  diagram,  similar  to  the  one 
for  the  cubic  system,  page  20,  expresses  very  clearly  the  relationship 
existing  between  the  various  forms. 


oo  a  :  oo  a  :  °°  a  :  c 


a  :  co  a  :  a  :  me        2a  :  2a  :  a  :  me 

\  / 

na  :  pa  :  a  :  me 


a  :  oo  a •  :  a  : 


-2a  :  2a  :  a  :  °°  c 


-na  :  pa  :  a  :  °°c 

Combinations. — The  following  figures  illustrate  some  of  the  combina 
tions  of  forms  of  this  class. 

Figure  134,  p  =  (a  :  <*a  :  a  :  c),  {lOll};  w  =  (2a  :  2a  :  a  :  c),  {1122}. 
Figure  135,  m  =  (a  :  ooa  :a  :  °°c),  jlOlO};  p  =  (a  :  ooa  :  a  :  c),  {lOTlj. 


FIG.   134. 


FIG.   135. 


FIG.   136. 


Figure  136,  m  =  (a  :  °°a_:  a  a>c),  {1010};  a  =  (2a  :  2a  :a  :  <»<•),  {1120}; 

p  =  (a  :  coa  :a  :  c),  {lOll};  s  =  (2a  :  2a  :  a  :  2c),  {1121};  c  =  (°oa  : 

oo  a  :  ooa  :  c),  {0001}.  This  combination  is 
observed  on  beryl  (Be3Al2Si6Oi8). 

DITRIGONAL  SCALENOHEDRAL  CLASS1 

Symmetry. — The  symmetry  consists  of  three 
intermediate  planes,  three  axes  of  binary  and 
one  of  trigonal  symmetry,  and  the  center  of 
symmetry.  The  binary  axes  are  the  lateral 
crystallographic  axes.  The  principal  crystallo- 
graphic,  or  c,  axis  possesses  trigonal  symmetry. 
Figure  137  shows  the  distribution  of  these 

elements  of  symmetry.     This  class  contains  two  forms  which  are  mor- 
phologically new,  rhombohedrons  and  scalenohedrons. 

Rhombohedrons. — These  are  bounded  by  six  rhombic  faces  inter- 
secting in  eight  trihedral  angles.     The  c  axis  passes  through  the  two  equal 
trihedral  angles  which  may  be  either  larger  or  smaller  than  the  other  six 
1  Dana  terms  this  class  the  rhombohedral  group. 


FIG.   137. 


HEXAGONAL  SYSTEM 


39 


which  among  themselves  are  equal.  The  size  of  these  angles  depends 
upon  the  value  of  the  ratio  a  :  c. l  This  is  illustrated  by  Figs.  138,  139 
and  140.  Positive  (Figs.  139  and  140)  and  negative  (Fig.  138)  rhornbo- 
hedroQS  are  possible.  In  the  positive  form,  the  upper  dodecant  to  the 


FIG.   138. 


FIG.   139. 


FIG.   140. 


front  possesses  a  face;  in  the  negative  an  edge.  The  symbols  are:  ± 
(a  :  co a  :  a  :  me),  or  {hohl}  and  {ohhl}.  These  ratios  correspond  to 
those  of  the  hexagonal  bipyramids  of  the  first  order,  page  32. 

The  principal  crystallographic  axis  passes  through  the  two  equal 
trihedral  angles.  The  lateral  axes  bisect  opposite  lateral  edges  which 
form  a  zigzag  line  about  the  form.  These  axes  possess  trigonal  and  binary 

1  The  cube,  when  held  so  that  one  of  its  axes  of  trigonal  symmetry,  page  17,  is 
vertical,  may  be  considered  as  a  rhombohedron  whose  edges  and  angles  are  equal. 
The  ratio,  a:  c,  in  this  case  would  be  1:  \/1.5  =  1:  1.2247-f.  Those  rhombohedrons, 
therefore,  whose  c  axes  have  a  greater  value  than  1.2247+  have  pole  angles  less  than 


FIG.  141. 


FIG.  142. 


90°.  When,  however,  the  value  is  less  than  1.2247+,  the  pole  angles  are  then  greater 
than  90°  and,  hence,  such  rhombohedrons  may  be  spoken  of  as  acute  and  obtuse, 
respectively,  Figs.  141  and  142. 


40 


MINERALOGY 


symmetry,  respectively.  The  intermediate  planes  of  symmetry  bisect 
the  various  faces  vertically. 

Scalenohedrons. — These  forms  are  bounded  by  twelve  similar 
scalene  triangles  intersecting  in  six  obtuse  and  six  more  acute  polar 
edges  and  in  six  zigzag  lateral  edges.  The  forms  are  congruent  and  hence 
may  be  positive,  Figs.  144  and  145,  or  negative,  Fig.  143,  in  character. 
As  is  the  case  with  the  rhombohedrons,  obtuse  and  acute  scalenohedrons 
are  also  possible,  depending  upon  the  value  of  a  :  c. 

The  symbols  are  ±  (na  :  pa  :  a  :m,c),  or  \hikl}  and  \ihkl}.  These 
symbols  correspond  to  those  of  the  dihexagonal  bipyramids,  page  34. 

Scalenohedrons  with  twelve  equal  polar  edges  are  crystallographically 
impossible  as  such  forms  would  possess  irrational  coefficients. 

The  axis  of  trigonal  symmetry  passes  through  the  two  hexahedral 
angles,  while  those  of  binary  symmetry  bisect  the  zigzag  lateral  edges. 
The  intermediate  planes  of  symmetry  pass  through  the  polar  edges. 


FIG.   143. 


FIG.   144. 


FIG.  145. 


Other  Forms. — The  other  forms  of  this  class  are  the  hexagonal  bi- 
pyramids of  the  second  order,  the  hexagonal  prisms  of  the  first  and  second 
orders,  the  dihexagonal  prism,  and  the  basal  pinacoid  all  of  which  are 
exactly  similar  to  those  of  the  dihexagonal  bipyramidal  class. 


Planes 

Axes 

Horizontal 

Vertical 

Vertical 

Horizontal 

Center 

Sym- 

metry 

Axial 

Axial 

Intermediate 

A 

Axial 

Axial 

Intermediate 

HEXAGONAL  SYSTEM 


41 


Forms 

Symbols 

i 
* 
fe 

Solid  angles 

Weiss 

Miller- 
Bra  vais 

Trihedral 

Tetraliedral 

Hezahedral 

Rhombohedrons 

;  \  'v 

+  a  :  oo  a  :  a  :,mc 

[hohl] 
{ohhl} 

}6 

2-H6 

- 

Hexagonal 
Bipyramid 
Second  order 

2a:  2a:  a:  me 

{hh2hl} 

Morphologically  the  same  as  in 
the    dihexagonal     bipyramidal 
class. 

Scalenohedrons 

±  na:  pa:  a:  me 

(hikl\ 
\ihkl\ 

\12 

> 

— 

6 

2 

•» 

Hexagonal  Prism 
_..            ,                       a:  <*>a:  a:  c°c 
First  order 

{hoho} 

Morphologically   the  same   as 
^      in     the     dihexagonal    bipy- 
ramidal class. 

Hexagonal  Prism             2a:  2«:  a:  ~c 
Second  order 

{1120} 

Dihexagonal  Prism         na  :  pa  :  a  :  °°  c 

{hikol 

Basal  Pinacoid                °°  a  :  °°  a  :  °°  a  :  c 

{0001} 

Combinations. — Many  important  minerals  crystallize  in  this  class, 
for  example,  calcite,  hematite,  corundum,  and  chabazite. 


FIG.  146. 


FIG.  14  . 


FIG.   148. 


Figures  146  to  149,  m  =  (a:  °°a  :a  :  <*>_c),  {1010};  e  =  -(a  :  <*>  a: 
a:^c),  {0112} ;  v  =  (%o_:  3a:  a:  3c),  {2131};  r  (a:  ooa:a:c),  {1011}; 
f  =  —  (a  :  oo  a:  a:  2c),  {0221}.  These  combinations  are  frequently  ob- 
served on  calcite  (CaCO3). 

Figures  150  and  151,  r  =  (a  :«ra:a:c),  (lOTl);  n  =  (2a:  2a:  a:  ^c), 
{2243};  u  =  (a  :  ™a  :a  :>^c),  {1014};  c  =  (ooa:  coa:  ooa:c),  {0001}. 
Hematite  (Fe2O3). 


42 


MINERALOGY 


Figures  152 and  153,  a  =  (2a_:  2a:  a:  ooC);  {1120};  n  =  (2a:2a:o:^c) 

(2243);  r  =  (a:  coa:a:c),     {1011}:  c  =  (oo«:  ooa:  «>a:c),     J0001}. 
Corundum  (A12O3). 


FIG.   149. 


FIG.  150. 


FIG.  151. 


FIG.   152. 


FIG.   153. 


FIG.  154. 


Figurel54,  r  =  (a:  coa:a:C),  {I011};e=   -  (a:  °°a:  a:  ^c),  {0112}  ; 
/=  -(a:  ooa:a:2c),    {0221}.     Chabazite   (CaAl2Si6O16.8H2O). 

HEXAGONAL  BIPYRAMIDAL  CLASS 

Symmetry. — Crystals  of  this  class  possess  the  horizontal  axial  or 
principal  plane,  the  hexagonal  axis,  and  the  center  of  symmetry.     The 


FIG.  155. 

hexagonal  axis  is  obviously  the  vertical  or  c  axis.     Figure  155  shows  the 
relation  of  these  elements  of  symmetry. 


HEXAGONAL  SYSTEM 


43 


This  class  contains  two  forms  which  are  new :  hexagonal  bipyramids 
and  prisms  of  the  third  order. 

Hexagonal  Bipyramds  of  the  Third  Order. — These  bipyramids 
are  analogous  to  those  of  the  first  and  second  orders  but  differ  from  them 
with  respect  to  their  orientation.  Their  symbols  correspond  to  those 
of  the  dihexagonal  bipyramids,  page  34,  namely :  +  (na  :  pa  :  a  :  me) 


FIG.  156. 


FIG.   157. 


and    [hikl]   or    {ihkl},    (Figs.   156  and    157.)     They  are    bounded    by 
twelve  equal  isosceles  triangles. 

The  axis  of  hexagonal  symmetry  passes  through  the  hexahedral 
angles.  The  position  of  the  lateral  crystallographic  axes  is  showr  in 
Figs.  158  and  159.  These  axes  do  not  pass  through  the  tetrahedral 
angles  or  the  centers  of  the  basal  edges,  as  is  the  case  with  the  forms  of 


FIG.  158. 


FIG.  159. 


the  first  and  second  orders,  respectively,  but  through  some  point  be- 
tween them  depending  upon  the  value  of  n.  Compare  Figs.  122  and  124. 
Hexagonal  Prisms  of  the  Third  Order. — These  forms  bear  the  same 
relation  to  those  of  the  first  and  second  order  as  do  the  hexagonal  bipyra- 
mids of  the  third  order  to  those  of  the  other  two  orders.  They  consist 
of  two  forms  of  six  planes  each,  designated  as  positive,  Fig.  161,  and 
negative,  Fig.  160.  Figures  158  and  159  show  the  relation  of  these 


44 


MINERALOGY 


forms  to  the  other  hexagonal  prisms.  Their  symbols  correspond  to  those 
of  the  dihexagonal  prisms,  page  37,  and  are  ± (na  :  pa  :  a  :  <»  c)  and 
{hiko}  or  {ihko}. 

The  hexagonal  axis  of  symmetry  is  parallel  to  the  vertical  edges. 


FIG.  160. 


FIG.  161. 


Other  Forms. — The  other  forms  of  this  class  are  the  hexagonal 
bipyramids  and  prisms  of  the  first  and  second  orders  and  the  basal 
pinacoid.  They  correspond  to  the  analagous  forms  of  the  dihexagonal 
bipyramidal  class. 

Summary. — The  principal  features  of  this  class  have  been  summarized 
in  the  following  table: 


Sym- 
metry 

Planes 

Axes 

1 

3 

Horizontal 

Vertical 

Vertical 

Horizontal 

Axial 

Axial 

Intermediate 

Axial 

• 

Axial 

Intermediate 

1 

0 

0 

1 

0 

0 

1 

HEXAGONAL  SYSTEM 


45 


Forms 

Symbols 

1 

Angles 

Weiss 

Mffler- 
Bravais 

i 

1*2 

Jl 

Hexagonal  Bipyramids 
First  order 

a:  oo  a:  a:  me 

{hohl} 

Morphologically 
like  in  dihexago- 
nal  bipyramidal 
class. 

Hexagonal  Bipyramids 
Second  order 

2a:  2a:  a:  me 

{hh2hl} 

Hexagonal  Bipyramids 
Third  order 

±  na:  pa:  a:  me 

{hikl} 
{ihkl} 

1- 

6 

2 

Hexagonal  Prism 
First  order 

a:  ooa;  a:  o°c 

{hoho} 

Morphologically 
like  in  dihexago- 
nal  bipyramidal 
class. 

Hexagonal  Prism 
Second  order 

2a  :  2a  :  a  :  oo  c 

{1120} 

Hexagonal  Prisms 
Third  order 

±  na:  pa:  a:  oo  c 

{hiko} 

{ihko} 

i 

6 

— 

— 

Basal  Pinacoid 

oo  a  :  oo  a  :  oo  a  :  c 

{0001} 

Morphologically 
like    in   dihexago- 
nal       bipyramidal 
class. 

Combinations. — Figures  162  and  163,  m  =  (a  :  <x>a  :  a  :  *>c), 
{1010} ;  a  =  (2a  :2a  :  a  :  ooc),  {1120};  p  =  (a  :  °°a  :  a  :  c)_f  {lOllj, 
y  =  (a  :  o>a  :a  :2c),  {2021};  r  =  (a  :  ooa  :  a  :  l/2c),  {10l2};  »  = 


FIG.  162. 


FIG.  163. 


(2o  :  2a  :  a  :  2c),  {1121};  M  =  (3/2a  :  3a  :  a  :  3c),  {2131};  c  =  (ooa  : 
ooa  :  ooa  :  c),  {0001}.  These  combinations  have  been  observed  on 
apatite  (Ca5Cl(PO4)3). 


46 


MINERALOGY 


DITRIGONAL  PYRAMIDAL  CLASS 

Symmetry. — There  are  three  intermediate  planes  and  one  trigonal 
axis  of  symmetry.  The  axis  of  symmetry  is  the  c  axis,  and  has  a  polar 
development.  The  forms  of  this  class,  therefore,  show  a  hemimorphic 
development,  that  is,  the  upper  and  lower  ends  of  the  c  axis  do  not  have 
the  same  type  of  faces.  The  symmetry  rela- 
tions are  shown  in  Fig.  164.  The  following 
forms  are  morphologically  different  from  those 
previously  described:  trigonal  pyramids  and 
prisms  of  the  first  order  and  ditrigonal  pyramids 
and  prisms. 

Since  the  c  axis  has  a  polar  development,  all 
forms  cutting  it,  will  occur  as  upper  and  lower 
forms.     Thus,  instead  of  having  bipyramids,  as 
usually  is  the  case,  we  now  have  upper  and  lower  pyramids. 

Trigonal  Pyramids  of  the  First  Orcler. — These  are  bounded  by  three 
equal  isosceles  triangles.  They  are  open  forms  and  may  occur  in  four 
distinct  positions  designated  as: 

Positive  upper,    +u(a  :  «>a  :a  :  we);  {hohl}.  Fig.  167. 

Positive  lower,     +  l(a  :  «>a  :a  :  we);  {hohl}.  Fig.  168. 

Negative  upper,  —u(a  :  o°a  :  a  :mc);  {ohhl}.  Fig.  165. 

Negative  lower,   —l(a  :  <»a  :a  :  we);  {ohhl}.  Fig.  166. 


FIG.   164. 


FIGS.   165  and  166. 


FIGS.  167  and  168. 


FIG.  169. 


FIG.   170. 


HEXAGONAL  SYSTEM 


47 


These  symbols  correspond  to  those  of  the  hexagonal  bipyramids 
of  the  first  order,  page  31.  The  axis  of  trigonal  symmetry  passes 
through  the  trihedral  angle  with  equal  edges  and  the  intermediate  planes 
of  symmetry  bisect  the  faces. 


FIG.   171. 


FIG.   172. 


Trigonal  Prisms  of  the  First  Order. — These  prisms  possess  three  faces 
and  occur  in  positive  (Fig.  172)  and  negative  (Fig.  171)  forms. 
The  symbols  are: 

±  (a  :  oo  a  :  a  :  co  c)  or  { hoho }  and  { ohho } . 

The  trigonal  axis  is  parallel  to  the  intersection  lines  of  the  prism 
faces  and  the  intermediate  planes  of  symmetry  pass  through  the  vertical 
edges  and  the  centers  of  the  opposite  faces.  Figures  169  and  170  show 
the  positions  of  the  various  trigonal  pyramids  and  prisms  with  respect 
to  the  crystallographic  a  axes. 

Ditrigonal  Pyramids. — These  pyramids  are  also  open  forms  and  are 
bounded  by  six  scalene  triangles.  Four  distinct  positions  are  possible. 

Their  symbols  are: 

+u(na  :  pa  :  a  :  me),  {hikl}. 
-\-l(na  :pa  :a  :  me),  {hikl}. 


Positive  upper, 

Positive  lower, 

Negative  upper,  —  u(na  :  pa  :  a  :  me),  {ihkl} 

Negative  lower,    —l(na  :  pa  :  a  imc),  {Ml} 


Fig.  175. 
Fig.  176. 

Fig.  173. 

Fig.  174. 

The  trigonal  axes  pass  through  the  hexahedral  angles  and  the  inter- 
mediate planes  of  symmetry  include  an  obtuse  and  an  acute  edge. 

Ditrigonal  Prisms. — These  prisms  are  bounded  by  six  faces  intersect- 
ing in  edges  which  are  alternately  alike.  Positive  (Fig.  180)  and 
negative  (Fig.  179)  forms  are  possible. 

The  symbols  are: 

±  (na  :  pa  :  a  :  °o  c)  or  { hiko }  and  { ihko } . 

The  trigonal  axis  is  parallel  to  the  intersection  lines  of  the  prism 
faces  and  the  intermediate  planes  of  symmetry  join  opposite  edges  of 
unequal  character.  Figures  177  and  178  indicate  the  position  of  the 
ditrigonal  pyramids  and  prisms  with  respect  to  the  a  axes. 


48 


MINERALOGY 


FIGS.  173  and  174. 


FIGS.  175  and  176. 


FIG.  177. 


FIG.  178. 


FIG.  179. 


FIG.  180. 


Basal  Pinacoids. — On  account  of  the  fact  that  the  c  axis  has  a  polar 
development,  the  basal  pinacoids  occur  with  but  one  face  (Fig.  165  to 
168).  We  may  therefore  speak  of  an  upper  and  a  lower  basal  pinacoid. 

The  symbols  are: 

u,  I  (ooa  :  coa  :  coa  :  c)  or  {0001}  and  {0001} 

Hexagonal  Pyramids  of  the  Second  Order. — These  forms  are  the 
upper  and  lower  portions,  respectively,  of  the  hexagonal  bipyramid  of  the 
second  order  described  on  page  33, 


HEXAGONAL  SYSTEM  49 

The  symbols  are: 

u,  I  (2a  :  2a  :  a  :  me)  or  {hh2hl\  and  {hh2hl\. 

Hexagonal  Prisms  of  the  Second  Order. — This  form  is  identical  mor- 
phologically with  that  described  on  page  36. 

Summary. — The  following  table  shows  the  principal  features  of  the 
forms  of  this  class: 


Symmetry 

Planes 

Axes 

Horizontal 

Vertical 

Vertical 

Horizontal 

Axial 

Axial 

Intermediate 

A 

Axial 

Axial 

Intermediate 

0 

0 

o 

1 
(Polar) 

0 

0 

Symbols 


Solid  angles 


Forms 

Number  of  f 

1 

!    1 

H            a 

Weiss 

Miller- 
Bra  vais 

Trigonal  Pyramids 
First  order 

±M,  ±1,  a:  co  a:  a:  me 

{hohl} 
\hohl] 
\ohhl] 
\ohhl} 

1 

3 

i 

— 

Hexagonal  Pyramids 
Second  order 

u,  I,'  2a:  2a:  a:  me 

\hh2hl} 
[hh2kl\ 

6 

— 

i 

Ditrigonal  Pyramids 

±u,  ±1,  na:  pa:  a:  me 

{hikl} 
\hikl} 
[ihkl] 
{ihkl} 

6 

— 

i 

Trigonal  Prisms 

±a:ooa:  arooc 

\hoho] 
\ohho} 

3 

Ditrigonal  Prisms 

±na:  pa:  a:  me 

\hiko} 
\ihko  } 

6 

— 

Hexagonal  Prism 
Second  order 

2a:2a:a:ooC 

\hh2ho\ 

Morphologically    like    in    di- 
hexagonal  bipyramidal  class. 

Basal  Pinacoids 

u,  1,  oo  a  :  oo  a  :  oo  a:  c 

{0001} 
{OOOT} 

1 

— 

— 

50 


MINERALOGY 


Combinations. — The  mineral  tourmaline  furnishes  excellent  combi- 
nations of  the  above  forms. 


FIG.  181 


FIG.   182. 


In  the  accompanying  Figs.  181  and    182  m  = 
{1010};    a   =    (2a  :  2a  :  a  :  a>c),    {1120}  ;  u  =   +u 
{3251}  ;o=  -u(a  :  ooa  :  a  i2c)t  {0221  }  ;  o'  =  +  l(a  : 
r  =  -l(a  :  ooa  :  a  :  c),  {OlTT};  c  =  /(ooa  :  ooa  :  ooa 
combinations  are  observed  on  tourmaline. 


(a  :  ooa  :  a  :  ooc), 

a  :  %a  :  a  :_5c), 

a  :a  :2c)  {202TJ; 

c),  (0001).   These 


TRIGONAL  TRAPEZOHEDRAL  CLASS 

Symmetry. — The  c  axis  possesses  trigonal  symmetry,  while  the  lateral 
or  a  axes  have  binary  symmetry  with  a  polar  development.  The  sym- 
metry relations  are  given  in  Fig.  183. 


FIG.   183. 

The  trigonal  trapezohedrons  are  the  characterizing  forms  of  this  class. 
Rhombohedrons  of  the  First  Order. — These  are  identical  morpholog- 
ically with  those  of  the  ditrigonal  scalenohedral  class. 
Their  symbols  are: 

+  (a  :  oo  a  :  a  :  me)  or  { hohl }  and  { ohhl } . 

Trigonal  Bipyramids  of  the  Second  Order. — These  forms  are  bounded 
by  six  equal  isosceles  triangles  and  possess  the  following  symbols: 

±  (2a  :  2a  :  a  :  me)  or  {hh2hl}  and  {2hhhl}. 


HEXAGONAL  SYSTEM 


51 


The  crystallographic  a  axes  pass  from  a  tetrahedral  angle  to  the  center 
of  the  opposite  horizontal  edge. 

Trigonal  Trapezohedrons.^There  are  four  forms  of  this  type  pos- 
sible. Each  is  bounded  by  six  faces,  which  when  the  development  is 


FIG.   184. 


FIG.   185. 


FIG.   186. 


FIG.   1ST. 


ideal,  are  equal  trapeziums.     The  symbols  are  analogous  to  those  of  the 
dihexagonal  bipyramids,  namely, 

1.  Positive  right,  -j-r(na  :  pa  :  a  :  me),  {hikl},  Fig.  185. 

2.  Positive  left,  +l(na  :  pa  :  a  :  me),  [kihl],  Fig.  184. 

3.  Negative  right,  —r(na  :  pa  :  a  :mc),  {ihkl},  Fig.  187. 

4.  Negative  left,  —  l(na  :  pa  :  a  :  me),  {khll},  Fig.  186. 

Forms  1  and  2,  3  and  4  are  among  themselves  enantimorphous,  while 
1  and  3,  2  and  4  are  congruent. 

The  polar  axes  of  binary  symmetry  bisect  the  zigzag  edges. 


52 


MINERALOGY 


Trigonal  Prisms  of  the  Second  Order. — These  possess  three  vertical 
planes  and  have  the  following  symbols : 

±(2a  :2a  :a  :  c°c)  or  {hh2ho}  and  {2hhho}. 

The  binary  axes  of  symmetry  pass  from  a  vertical  edge  through  the 
center  of  the  opposite  face. 

Ditrigonal  Prisms. — Two  forms  of  this  type  are  possible  and  desig- 
nated as  right  (Fig.  189)  and  left  (Fig.  188)  ditrigonal  prisms.  The 
vertical  edges  are  alternately  alike. 

The  symbols  are: 

+  (na  :  pa  :  a  :  <*>c  )or  \hiko}  .and  \kiho}. 


FIG.   188. 


FIG.  189. 


Other  Forms.  The  hexagonal  prism  of  the  first  order  and  the  basal 
pinacoid  are  analogous  to  those  described  on  pages  36  and  37. 

Summary. — The  important  features  of  this  class  are  given  in  the 
following  table. 


Symmetry 

Planes 

Axes 

S 

o 

0 

Horizontal 

Vertical 

Vertical 

Horizontal 

Axial 

Axial 

Intermediate 

A 
Axial 

Axial 

Intermediate 

0 

0 

0 

1 

3 

0 

0 

(Polar) 

HEXAGONAL  SYSTEM 


53 


Forms 

Symbols 

s 

i 

Solid  angles 

Trihedral 

Tetra- 
hedral 

Weiss 

Miller- 
Bra  vais 

Rhombohedrons 
First  order 

±a:  coa:a:mc 

\hohl} 
{ohhl} 

1 

i- 

Morphologically 
like    those    in    the 
ditrigonal  scaleno- 
bedral  class. 

Trigonal  Bipyramids 
Second  order 

±2a:  2a:  a  :  me 

{hh2hl\ 
[2hhhl] 

}« 

2 

3 

Trigonal  Trapezohedrons 

+  r,  +1,  na:  pa:  a:  me 

{hikl} 
{Ml} 
{ihkl} 
\khil\ 

6 

2 

+ 
6 

Hexagonal  Prism 
First  order 

a:  coa:  a:  ooc 

{hoho} 

6 

1~ 
}« 

Morphologically 
like  those  in  the  di- 
hexagonal   bipyra- 
midal  class. 

Trigonal  Prisms 
Second  order 

+  2a:  2a:  a:  °°c 

\M2ho} 
{2hhho} 





Ditrigonal  Prisms 

+  na:  pa:  a:  co  c 

\hiko] 
\klho  \ 

Basal  Pinacoid 

coa:  coa:  o°a:  c 

{0001} 

2 

Morphologically 
like  those  in  the  di- 
hexagonal       bipy- 
ramidal  class. 

Combinations. — Quartz,  SiO2,  and   cinnabar,  HgS,  furnish  excellent 
examples  of  minerals  crystallizing  in  this  class. 


FIG.  190. 


FIG.   191. 


Figures  190  and  191.     m  =  (a  :  °°a  :  a  :  ooc),  {1010}; 

r  =  +(a  :  coa  :a  :  c),   {lOll};  z  =  -(a  :  coa  :a  :  c),   {OlTl}; 


54  MINERALOGY 

s(Fig.  191)  =  +(2a  :2a  :a  :  2c),  {1121};  «(Fig.  190)  =  ~(2a  :2a  : 
a:2c),  {2111};  a;  (Fig.  191)  =_  +r(%a  :  6a  :  a  :  6c),  {5161};  z(Fig. 
190)  =  -/(%a  :  6a  :  a  :  6c),  {6151}.  Quartz. 

Figures  192  and  193.  c  =  (°°a  :  <*>a  :  *>a  :  c),  {0001};  m  =  (a  : 
ooa  :a  :  ooC),  {lOlOj;  g  =  -(a  :  «>a  :a  :  J£c),  {Oll2};  n  =  -(a  :  ™a  : 


FIG.   192.  FIG.   193. 

a  :2c),    {0221};  ^  =  -(a  :  ooa  :a  :%c),  {0223};  r  =  +(o  :  o°a  :o  :c), 
{1011};    /  =    -(a  :  *>a  :  a  :c),      {OlTlj;     y  -  +r(%a  :  3a  :  a  : 
(2137J ;  x  =  +l{%a  :  %a  :  a  :  %c),   {8355).     Cinnabar. 


CHAPTER  IV 
TETRAGONAL  SYSTEM1 

Crystallographic  Axes. — The  tetragonal  system  includes  all  crystals 
which  can  be  referred  to  three  perpendicular  axes,  two  of  which  are 
equal  and  lie  in  a  horizontal  plane.  These  are  termed  the  lateral  axes 
and  are  designated  as  the  a  axes.  Perpendicular  to  the  plane  of  the  lateral 
axes  is  the  principal  or  c  axis,  which  may  be  +c 

longer  or  shorter  than  the  a  axes.  The  axes, 
which  bisect  the  angles  between  the  a  axes, 
are  the  intermediate  axes.  They  are  desig- 
nated as  the  b  axes  in  Fig.  194. 

Crystals  of  this  system  are  held  so   that    __  ^ 

the  c  axis  is  vertical  and  one  of  the  a  axes  is  *~+«^ 

directed  towards  the  observer. 

Since  the  lengths  of  the  a  and  c  axes 
differ,  it  is  necessary  to  know  the  ratio  exist- 
ing between  these  axes,  that  is,  the  axial  ratio, 
as  was  the  case  in  the  hexagonal  system.  Com- 
pare pages  6  and  30. 

Classes  of  Symmetry. — This  system  embraces  seven  classes  of  sym- 
metry, as  follows: 

1.  Ditetragonal  bipyramidal  class. 

2.  Ditetragonal  pyramidal  class. 

3.  Tetragonal  scalenohedral  class. 

4.  Tetragonal  bipyramidal  class. 

5.  Tetragonal  trapezohedral  class. 

6.  Tetragonal  pyramidal  class. 

7.  Tetragonal  bisphenoidal  class. 

Classes  1  and  3  are  the  most  important  and  will  be  discussed  in  detail. 
No  representative  of  class  7  has  yet  been  observed. 

DITETRAGONAL  BIPYRAMIDAL  CLASS2 

Symmetry,  (a)  Planes. — In  this  class  there  are  five  planes  of  sym- 
metry. The  plane  of  the  lateral  and  intermediate  axes  is  termed  the 
horizontal  axial  or  principal  plane.  The  vertical  planes  including  the  c 

1  Also  termed  quadratic  or  pyramidal  system. 

2  The  normal  group  of  Dana. 

55 


56 


MINERALOGY 


and  one  of  the  a  axes  are  called  the  vertical  axial  planes,  while  those  which 
include  one  of  the  b  axes  are  termed  the  intermediate  planes,  Fig.  195. 

The  three  axial  planes  divide  space  into  eight  equal  parts,  termed 
octants.  The  five  planes,  Fig.  195,  divide  it  into  sixteen  equal  sections. 
The  five  planes  may  be  designated  as  follows: 

1  Horizontal  axial  +  2  Vertical  axial  +  2  Intermediate  =  5  Planes. 


-l-r-. 


FIG.  195. 


FIG.  196. 


FIG.  197. 


(b)  Axes.^-The  c  axis  is  an  axis  of  tetragonal  symmetry.     The  lateral 
and  intermediate  axes  possess  binary  symmetry,  Fig.  196.     These  may 
be  written:  1  •  +  2  •  +  2  •   =5  axes. 

(c)  Center. — A  center  of  symmetry  is  also  present  in  this  class.     These 
elements  of  symmetry  are  shown  in  Fig.  197,  which  represents  the  pro- 
jection of  the  most  complex  form  upon  the  principal  plane  of  symmetry. 

Tetragonal  Bipyramid  of  the  First  Order. — This  form  is  analogous  to 
the  octahedron  of  the  cubic  system,   page  16.     But  since  the  c  axis 


FIG.   198. 


FIG.   199. 


differs  from  the  lateral  axes,  the  ratio  must  be  written  (a  :  a  :  c),  which 
would  indicate  the  cutting  of  all  three  axes  at  unit  distances,1  Figs.  198 
and  199.  As  the  intercept  along  the  c  axis  may  be  longer  or  shorter 
than  the  unit  length,  the  general  symbols  would  be  (a  :a:  me)  or  {hhl} 
where  m  is  some,  value  between  zero  and  infinity.  Like  the  octahedron, 


1  Indicating  a  unit  form,  compare  page  5. 


TETRAGONAL  S  YS  TEM  57. 

this  form,  the  tetragonal  bipyramid,1  is  bounded  by  eight  faces  which 
enclose  space.  The  faces  are  equal  isosceles  triangles  when  the  develop- 
ment is  ideal. 

The  principal  crystallographic  axis  passes  through  the  two  tetra- 
hedral  angles  of  the  same  size,  the  lateral  axes  through  the  other  four 
equal  tetrahedral  angles,  while  the  intermediate  axes  bisect  the  hori- 
zontal edges. 

Tetragonal  Bipyramid  of  the  Second  Order. — The  faces  of  this 
form  cut  the  c  and  one  of  the  a  axes,  but  extend  parallel  to  the  other. 
The  symbols  are  therefore,  (  a  :  <»  a  :  me)  or  { hoi } .  Eight  faces  are  required 
to  enclose  space  and  the  form  is  termed  the  bipyramid  of  the  second  order, 
Figs.  200  and  201.. 


FIG.  200.  FIG.  201. 

This  bipyramid  is  very  similar  to  the  preceding,  but  can  be  readily 
distinguished  from  it  on  account  of  its  position  with  respect  to  the  lateral 
axes.  In  this  form,  the  lateral  axes  bisect  the  horizontal  edges  and  the 
intermediate  axes  pass  through  the  four  equal  tetrahedral  angles.  This 
is  the  opposite  of  what  was  noted  with  the  bipyramid  of  the  first  order, 
compare  Figs.  198  and  199.  Hence,  the  bipyramid  of  the  first  order 
is  always  held  so  that  an  edge  is  directed  toward  the  observer,  whereas 
the  bipyramid  of  the  second  order  presents  a  face.  In  both  bipyramids 
the  principal  axis  passes  through  the  two  equal  tetrahedral  angles. 

Ditetragonal  Bipyramid. — The  faces  of  this  bipyramid  cut  the  two 
lateral  axes  at  different  distances,  while  the  intercept  along  the  c  axis 
may  be  unity  or  me.  Sixteen  such  faces  are  possible,  and  hence,  the  term 
ditetragonal  bipyramid  is  used,  Figs.  202  and  203. 2 

The  symbols  are : 

(a  :  na  :  me)  or  {hkl} . 

1  The  more  the  ratio  a  :  c  approaches  1:1,  the  more  does  this  form  simulate  the 
octahedron.     This  tendency  of  forms  to  simulate  those  of  a  higher  grade  of  symmetry 
is  spoken  of  as  pseudosymmetry. 

2  Compare  Fig.  34,  page  9. 


58 


MINERALOGY 


Since  the  polar  edges1  are  alternately  similar  it  follows  that  the 
faces  are  equal,  similar  scalene  triangles.  The  ditetragonal  bipyramid 
possessing  equal  polar  edges  is  crystallographically  an  impossible  form, 
for  then  the  ratio  a  :  na  :  me  would  necessitate  a  value  for  n  equal  to  the 
tangent  of  67°  30',  namely,  the  irrational  value  2.4142+.2 


FIG.   202. 


FIG.  203. 


From  the  above  it  follows  that  when  n  is  less  than  2.4142+  the 
ditetragonal  bipyramid  simulates  the  tetragonal  bipyramid  of  the  first 
order,  and  finally  when  it  equals  1,  it  passes  over  into  that  form.  On  the 
other  hand,  if  n  is  greater  than  2.4142+  it  approaches  more  the  bi- 
pyramid of  the  second  order,  and  when  it  is  equal  to  infinity  passes  over 
into  that  form.  Hence,  n>  1  <  oo .  Figure  204  illustrates  this  clearly. 


FIG.  204. 


FIG.  205. 


It  is  also  to  be  noted,  that  when  n  is  less  than  2.4142+  the  lateral  axes 
pass  through  the  more  acute  angles,  whereas,  when  n  is  greater  than 
2.4142+  they  join  the  more  obtuse.  Outline  1  represents  the,  cross- 
section  of  the  tetragonal  bipyramid  of  the  first  order,  2  that  of  the  second 
order,  and  3,  4  and  5  ditetragonal  bi pyramids  where  n  equals  %,  3, 
and  6,  respectively. 

1  Compare  footnote,  page  35. 

2  See  also  page  36. 


TETRAGONAL  SYSTEM  59 

Tetragonal  Prism  of  the  First  Order. — If  the  value  of  the  intercept 
along  the  c  axis  in  the  tetragonal  bipyramid  of  this  order  becomes  infinity, 
the  number  of  the  faces  of  the  bipyramid  is  reduced  to  four  giving  rise  to 
the  tetragonal  prism  of  the  first  order,  Fig.  205.  This  is  an  open  form 
and  possesses  the  following  symbols: 

(a  :a  :  ooc)  or  {110}. 

The  lateral  axes  join  opposite  edges,  hence,  an  edge  is  directed  toward 
the  observer. 

Tetragonal  Prism  of  the  Second  Order. — The  same  relationship  exists 
between  this  form  and  its  corresponding  bipyramid  as  was  noted  on  the 
preceding  form. 
The  symbols  are: 

(a  :  coa  :  co£)  or  {100}. 


FIG.  206.  Fin.  207. 

This  is  also  an  open  form  consisting  of  four  faces,  Fig.  206.  The 
lateral  axes  join  the  centers  of  opposite  faces.  Hence,  a  face  is  directed 
toward  the  observer. 

Ditetragonal  Prism. — As  is  obvious,  this  form  consists  of  eight  faces 
possessing  the  following  symbols: 

( a  :  na  :  oo  c)  or  { hko } . 

What  was  indicated  on  page  58  concerning  the  polar  angles  and  the 
position  of  the  lateral  axes  applies  here  also.  Figure  207  represents  a 
ditetragonal  prism. 

Basal  Pinacoid. — This  form  is  similar  to  that  of  the  hexagonal  sys- 
tem, page  37.  It  is  parallel  to  the  lateral  axes  but  cuts  the  c  axis.  The 
symbols  may  be  written : 

(ooa  :  ooa  :  c),  OP,  {001}. 

This  form  consists  of  but  two  faces.  They  are  shown  in  combination 
with  the  three  prisms  in  Figs.  205,  206,  and  207. 

Summary. — The  seven  forms  in  this  class  and  the  chief  character- 
istics are  given  in  the  following  table: 


MINERALOGY 


Symmetry 

Planes 

Axes 

Center 

Horizontal 

Vertical 

Vertical 

Horizontal 

Axial 

Axial 

Intermediate 

• 
Axial 

Axial 

Intermediate 

1 

2 

2 

1 

2 

2 

1 

Symbols 


Solid  angles 


Jborms 

Weiss 

Miller 

.paces 

Tetrahedral 

Octahedral 

Unit  Bipyramid 
First  order 

a:  a:  c 

{111} 

8 

2+4 

— 

Modified    Bipyra- 
mids  First  order 

a:  a:  me 

[hhl] 

8 

2+4 

— 

Bipyramids 
Second  order 

a:  °°a:  me 

\hol\ 

• 

2+4 

— 

Ditetragonal 
Bipyramids 

a:  na:  me 

{hkl} 

16 

4+4 

2 

Prism 
First  order 

a:  a:  c°c 

{110} 

4 

— 

— 

Prism 
Second  order 

a:  oo  a  :  oo  c 

{100} 

4 

—  ' 

— 

Ditetragonal 
Prisms 

a:  na:  oo  c 

{hko} 

8 

— 

— 

Basal  Pinacoid 

°°a:  co  a:  c 

{001} 

2 

— 

— 

Relationship  of  Forms. — This  is  clearly  expressed  by  the  following 
diagram.     Compare  pages  20  and  38. 


co  a  :  ooa  :  c 


a  :  co  a  :  me 


a :  a  :  me 


a  :  na  :  me 


a  :  ooa  :  <x»c 


a  :  a 


TETRAGONAL  SYSTEM 


61 


Combinations. — Some  of  the  more  common  combinations  are  illus- 
trated by  the  following  figures: 

Figures  208  to  211,  m  =  (cf:  a  :  «c),  (110);  p  =  (a  :  a  :  c),  {111}; 
a  =  (a  :  coa  :  coc),  {100};z  =  (a  :  3a  :  3c),  {311}.  These  combinations 
have  been  observed  on  zircon  (ZrSiO4). 


FIG.  208. 


FIG.  209. 


FIG.  210. 


FIG.  211. 


FIG.  212. 


FIG.  213. 


FIG.  214. 


FIG.  215. 


Figure  212,  m   =    (a  :  a  :  »c),    {110};  p   =    (a  :  a  :  c),    {111};  c   = 
(ooa  :  ooa  :  c),  {001}.     Vesuvianite,  Ca6[Al(OH;F)]  Al2(SiO4)5. 

Figure  213,  m    =    (a:a:ooC),    {110};  a    =    (a  :  <*>a  :  «c),    {100}; 
p  =  (a  :a  :  c),   Jill};  e  =  (a  :  a>a  :  c),   {101}. 
Observed  on  rutile  (TiO2). 

Figures   214   and   215,    a  =  (a  :  coa  :  <»c), 
{100};p  =  (a  :a  :c),  {lll};c=(ooa  :  ooa  :c), 
{001} ;    y    =     (a:3a:ooC),    {310}.     Apophyl-       / 
lite  (H14K2Ca8(SiO3)i6.9H2O). 

TETRAGONAL  SCALENOHEDRAL  CLASS 


FIG.  216. 


Symmetry. — This  class  possesses  two  inter- 
mediate planes  and  three  axes  of  binary  sym- 
metry.    One  of  the  axes  of  binary  symmetry  is  the  c  axis;  the  other 
two  are  the  a  axes.     This  is   clearly  illustrated  in  Fig.  216.     There 


62 


MINERALOGY 


are  two  forms  in  this  class  which  are  morphologically  new,  namely,  the 
tetragonal  bisphenoids  and  scalenohedrons. 

Tetragonal  Bisphenoids. — These  forms  consist  of  two  types,  positive 
(Fig.  218)   and  negative  (Fig.  217),  each  bounded  by  four  equal  isos- 


FIG.  217. 


FIG.  218. 


celes  triangles.     Their  symbols  are  analagous  to  those  of  the  tetragona 
bipyramids  of  the  first  order,  namely: 

±  (a  :  a  :  me)  or  { hhl }  and  { hhl } . 

The  a  axes  bisect  the  four  edges  of  equal  length,  while  the  c  axis  passes 
through  the  centers  of  the  other  two. 

Tetragonal  Scalenohedrons. — These  consist  of  eight  similar  scalene 
triangles  and  are  termed  positive  (Fig.  220)  and  negative  (Fig.  219)  forms. 

Their  symbols  are : 

+  (a  :  na  :  me)  or  { hkl }  and  { hkl } . 


FIG.  219. 


FIG.  220. 


These  symbols  correspond  to  those  of  the  ditetragonal  bipyramids,  page 
57.  The  c  axis  joins  those  tetrahedral  angles  which  possess  two  pairs 
of  equal  edges.  The  a  axes  bisect  the  four  zigzag  edges. 

Other  Forms. — The  tetragonal  bipyramids  of  the  second  order,  the 
tetragonal  prisms  of  the  first  and  second  orders,  the  ditetragonal  prisms. 


TETRAGONAL  SYSTEM  63 

and  the  basal  pinacoid  are  morphologically  identical  to  those  of  the  dite- 
tragonal  bipyramidal  class,  page  55. 

Summary. — The  characteristics  of  the  forms  of  the  tetragonal  scaleno- 
hedral  class  may  be  tabulated  as  follows: 


Planes 


Horizontal 

Vertical 

Vertical 

Horizontal 

Symmetry 

Axial 

Axial 

Intermediate 

Axial 

Axial     Intermediate 

0 

0 

2 

12                   0 

Solid  angles 


Symbols 

"3 

Forms 

03 

J 

-o 

(D 

Weiss                             Miller              § 

J: 

| 

^ 

h 

H 

Bisphenoids 
First  order 

\hhl] 

+  a:  a:  me 

\hhl\ 

4 

4 

Morphologically 

Bipyramid 
Second  order 

o.'.ooa:  me                    {hoi} 

like  in  ditetra- 
gonal      bip\Ta- 

midal  class 

{hkl} 

,. 

Tetragonal  Scalenohedrons                      +a~na-  me 

— 

2+4 

\hkl\ 

J 

Prism  —  First  order                                      a  :  a  :  oo  c                   {  1  1  0  } 

Prism  —  Second  order                                a  :  oo  a  :  oo  c                   {  1  00  } 

Morphologi- 
cally  like  in  di- 

Ditetragonal  Prisms 

(   tetragonal     bi- 
a:  na:<x>c                   \hf:o\                         .,  ,   , 
pyramidal  class 

Basal  Pinacoid                                          oo  a  :  oo  a  :  c                {  001  } 

64  MINERALOGY 

Combinations. — The  following   combinations,    Figs.    221    and    222, 


FIG.  221. 


FIG.  222. 


occur  on  chalcopyrite  (CuFeS2).   p  =  (a:  arc),  {111};  pf  =  - 
(a  :a  :  c>,  {111};  $  =  (a  :  a  :%c),  {772};  x  =  (a:2a  :  c),  {212}. 


CHAPTER  V 
ORTHORHOMBIC  SYSTEM1 

Crystallographic  Axes. — This  system  includes  all  crystals  which  can 
be  referred  to  three  unequal  and  perpendicular  axes  Fig.  223.  One 
axis  is  held  vertically,  which  is,  as  heretofore,  the  c  axis.  Another  is 
directed  toward  the  observer  and  is  the  a  axis,  sometimes  also  called  the 
brachyaxis.  The  third  axis  extends  from  right  to  left  and  is  the  b  axis  or 
macroaxis.  There  is  no  principal  axis  in  this  system,  hence  any  axis 
may  be  chosen  as  the  vertical  or  c  axis.  On  this  account  one  and  the 
same  crystal  may  be  held  in  different  positions  by  various  observers, 
which  has  in  some  instances  led  to  considerable  confusion,  for  as  is  ob- 
vious the  nomenclature  of  the  various  forms  cannot  then  remain  con- 


-c 
FIG.  223. 


FIG.  224. 


stant.     In  this  system  the  axial  ratio  consists  of  two  unknown  values, 
viz:  &  :b  :6  =  0.8130  : 1  :  1.9037,  compare  page  6. 

Classes  of  Symmetry. — The  orthorhombic  system  comprises  three 
classes  of  symmetry,  as  follows: 

1.  Orthorhombic  bipyramidal  class 

2.  Orthorhombic  pyramidal  class 

3.  Orthorhombic  bisphenoidal  class 

Numerous  representatives  of  all  these  classes  have  been  observed 
among  minerals  and  artificial  salts.  The  first  class  is,  however,  the  most 
important,  and  will  be  considered  in  detail. 


ORTHORHOMBIC  BIPYRAMIDAL  CLASS2 

Symmetry,  (a)  Planes. — There  are  three  axial  planes  of  symmetry, 
Fig.  224.  Inasmuch  as  these  planes  are  all  dissimilar,  they  may  be 
written : 

1  +  1  +  1  =  3  planes. 

1  Sometimes  termed  the  trimetric,  rhombic,  or  prismatic  system. 

2  The  normal  group  of  Dana. 

5  05 


66 


MINERALOGY 


(b)  Axes. — Three  axes  of  binary  symmetry  are  to  be  observed,  Fig. 
224.     They  are  the  crystallographic  axes  and  indicated  thus: 

1  •  +  •  1  +  1  •  =  3  axes. 

(c)  Center. — This  element  of  symmetry  is  also  present  and  demands 
parallelism  of  faces.     Figure  225  shows  the  above  elements  of  symmetry. 


FIG.  229. 

Orthorhombic  Bipyramids. — The  form  whose  faces  possess  the 
ratio,  (a  :  b  :  c) ,  or  { 1 1 1 } ,  is  known  as  the  unit  or  fundamental  orthorhombic 
bipyramid.  It  consists  of  eight  similar  scalene  triangles,  Fig..  226. 

The  outer  form,  in  Fig.  227,  possesses  the  ratio  (a  :  b  :  me)  or 
\hhl] ,  (ra>0<  oo ).  In  this  case  m  =  2.  This  is  a  modified  orthorhombic 
bipyramid. 


ORTHORHOMBIC  SYSTEM 


67 


In  Fig.  228,  the  heavy,  inner  form  is  the  unit  bipramid.  The  lighter 
bipyramids  intercept  the  b  and  c  axes  at  unit  distances  but  the  a  axis 
at  distances  greater  than  unity.  *  Their  ratios  may,  however,  be  indicated 
in  general  as, 

(nd  :b  :mc),  (n>l;  m>Q<  «)  or  {hkl}. 

These  are  the  brachybipyramids,  because  the  intercepts  along  the  brachy- 
axis  are  greater  than  unity. 


FIG.  230. 


Figure  229  shows  two  bipyramids  (outer)  which  cut  the  a  axis  at 
unity  but  intercept  the  b  axis  at  the  general  distance  nb,  (n>l).  The 
ratios  would,  therefore,  be  expressed  by  (a  :  nb  :  me).  Since  the  inter- 
cepts along  the  macroaxis  are  greater  than  unity,  these  are  called 
macrobipyramids. 


FIG.   231. 

Figure  230  shows  the  relationship  existing  between  the  unit,  macro-, 
and  brachybipyramids,  while  Fig.  231  shows  it  for  the  unit,  modified, 
and  macrobipyramids. 

Prisms. — Similarly  there  are  three  types  of  prisms,  namely,  the  unit, 
macro-,  and  brachyprisms  Each  consists  of  four  faces,  cutting  the  a 
and  b  axes,  but  extending  parallel  to  the  c  axis 


68  MINERALOGY 

Figures  232  and  233  represent  unit  prisms  with  the  following  symbols : 

(a  :b  :  <W)  or  {110}. 

The  brachyprism  is  shown  in  Fig  234.     Its  symbols  are: 
(nd  :b  :  °°6)  or  {hko}. 


FIG.  232. 


FIG.  233. 


In  Fig.  235,  there  is  a  unit  prism  surrounded  by  a  macroprism,  whose 
symbols  may  be  written : 

(a  :  nb  :  90 c)  or  {kho}. 

For  the  relationship  existing  between  these  three  prisms  compare 
Fig  230. 


FIG.  234. 


FIG  235. 


Domes. — These  are  horizontal  prisms  and,  hence,  cut  the  6  and  one  of 
the  horizontal  axes.  Domes,  which  are  parallel  to  the  d  or  brachyaxis 
are  called  brachydomes.  Their  general  symbols  are : 

(  co  a  :  6  :  me)  or  [ohl],  Fig.  236. 


ORTHORHOMRIC  SYSTEM 


69 


Those,  which  extend  parallel  to  the  macroaxis,  are  termed  macrodomes, 
Figs.  237  and  238.     Their  symbols  are: 

(a  :  oo  b  :  m6)  or  {hoi}. 

As  is  obvious,  prisms  and  domes  are  open  forms  and,  hence,  can  only 
occur  in  combination  with  other  forms. 


FIG.  236. 


FIG.    237. 


FIG.  238. 


Pinacoids. — These  cut  one  axis  and  extend  parallel  to  the  other  two. 
There  are  three  types,  as  follows: 

Basal  pinacoid,  (<*&  :  <*b  : 6)  or  (001). 
Brachypinacoid,  (*>&  :b:  &>£)  or  {OlOl. 
Macropinacoid,  (a  :  °°5  :  °°c)  or  {100}. 


1              ^^ 

\ 

i 

i 

i 

_._._^._._ 

— 

1 

i 

i 

i 

i  i  

_  

FIG.  239. 


FIG.  240. 


These  forms  consist  of  two  faces.  Figures  239  and  240  show  a  com- 
bination of  three  types  of  the  pinacoidsv 

Summary. — The  characteristics  of  the  forms  of  this  c'ass  are  given  in 
the  following  table : 


70 


MINERALOGY 


Symmetry 

Planes 

(axial) 

Axes 

Center 

1+1+1 

!•  +!•  +!• 

1 

Forms 

Symbols 

Faces 

Tetrahedral 

solid  angles 

Weiss 

•Miller 

Orthorhombic 
Bipyramids 

Unit 

dibit 

{111} 

8 

2+2+2 

Modified 

dibimc 

{hM} 

Brachy 

Macro 

ndibi  me 

{hkl\ 

dinbi  me 

{khl} 

Orthorhombic 
Prisms 

Unit 

dibi  ooc 

{110} 

4 

Brachy 

nd  i   b  i  oo  c 

{hko} 

Macro 

d  i  nbi  ooc 

{kho} 

Domes 

[Brachy 

oo  d  :  b  :  me 

{ohl\ 

4 

Macro 

di  cob  i  me 

{hoi} 

Pinacoids 

Basal 

oo  di  °°  6  i  c 

{001} 

2 

Brachy 

oo  d  i  b  i  <x>c 

{010} 

Macro 

di  cob:  ooc 

{100} 

Combination. — Figures  241  and  242,  p  =  (a  :b  :c),  {  111  };s  = 
(<*:&:Mc),  {113};  n  =  («>a:b:c),  {Oil} ;  c  =  (ooa  :  006  :  c),  {OOlJ. 
These  combinations  occur  on  native  sulphur. 


FIG.  241. 


Figure  243,  m  =  (a  :  b  :  ooC),  {110}  ;  b  = 
a  :  b  :  c),   {Oil}.     Aragonite  (CaCO3). 


FIG.  242. 

»a  :&  :  °°c),  {010}; 


ORTHORHOMBIC  SYSTEM 


71 


Figure     244,     m=(a:6:ooC),      {110};     1  =  (2o  :  b  :  »c),     (120); 
„  =  (a:6:c),  {111};*  =  (a  :  6  :  2/3c),    {223};    o  =  (a:6:2c),     {221}; 


FIG.  243. 


FIG.  244. 


y  =  (ooa  :6  :4c),  {041};  c  =  (»a  :  »6:c),  {001}.     Topaz  (A12(F.OH)2- 

Figure    245,     w=   (o  :  b  :  ooc),    {110J;    c«   (ooa:oo6:c),    {001}; 
d=   (a:  a,6:^c),    {102} ;    o  =  (ooa  :  6  :  c),     {Oil}.     Barite    (BaSO4). 


FIG.  245. 


FIG.  246, 


Figure    246,    m=(a:6:ooC),     {110};    u  =  («a  :  b  :  y±c);     {014} 
Arsenopyrite  (FeAsS\ 


CHAPTER  VI 
MONOCLINIC  SYSTEM1 

Crystallographic  Axes. — To  this  system  belong  those  crystals  which 
can  be  referred  to  three  unequal  axes,  two  of  which  (d  and  c)  inter- 
sect at  an  oblique  angle,  while  the  third  axis  (6)  is  perpendicular  to 
these  two.  The  oblique  angle  between  the  d  and  6  axes  is  termed  /3. 
Figure  247  shows  an  axial  cross  of  this  system. 


-c 
FIG.  247. 


FIG.  248. 


It  is  customary  to  place  the  5  axis  so  as  to  extend  from  right  to  left. 
The  c  axis  is  held  vertically.  The  d  axis  is  then  directed  toward  the  ob- 
server. Since  the  d  axis  is  inclined,  it  is  called  the  clinoaxis.  The  5 
axis  is  often  spoken  of  as  the  orthoaxis.  The  obtuse  angle  between  the 
d  and  6  axis  is  the  negative  angle  /3,  whereas  the 
acute  angle  is  positive.  Obviously,  they  are 
supplementary  angles.  The  elements  of  crystal- 
lization  consist  of  the  axial  ratio  and  the  angle  j3, 
which  may  be  either  the  obtuse  or  the  acute 
angle.  Compare  page  7. 

Classes  of  Symmetry. — The  monoclinic  system 
.  includes  three  classes  of  symmetry,  as  follows : 

1.  Prismatic  class. 

2.  Domatic  class. 

3.  Sphenoidal  class. 

The  first  class  is  the  most  important,  and  is  the  only  one  which  will 

be  considered. 

• 

1  Also  termed  the  clinorhombic,  hemiprismatic,  monoclinohedral,  monosymmetric 
or  oblique  system. 

72 


FIG.  249. 


MONOCLINIC  SYSTEM 


73 


MONOCLINIC  PRISMATIC  CLASS1 

Symmetry. — This  class  possesses  one  axial  plane  of  symmetry  (a  and  6 
axes).  It  is  directed  toward  the  observer.  Perpendicular  to  this  plane 
is  an  axis  of  binary  symmetry  (b  axis) .  A  center  of  symmetry  is  also  pres- 
ent. Figure  248  shows  these  elements  in  a  crystal  of  augite.  These 
elements  are  represented  diagrammatically  in  Fig.  249,  which  is  a  pro- 
jection of  a  monoclinic  form  upon  the  plane  of  the  a  and  6  axes. 

Hemi-bipyramids. — On  account  of  the  presence  in  this  class  of  only 
one  plane  of  symmetry  and  an  axis  of  binary  symmetry,  a  form  with 


FIG.  250. 


unit  intercepts,  that  is,  with  the  parametral  ratio  a  :  b  :  c,  can  possess 
but  four  faces.  Figure  250  shows  four  such  faces,  which  enclose  the 
positive  angle  /3  and  are  said  to  constitute  the  positive  unit  hemi-bipyr amid. 
Figure  251  shows  four  faces  with  the  same  ratio  enclosing  the  negative 
angle  /3,  and  comprising  the  negative  unit  hemi-bipyr  amid.  It  is  obvious 
that  the  faces  of  these  hemi-bipyramids  are  dissimilar,  those  over  the 


FIG.  252. 


FIG.  253. 


negative  angle  being  the  larger.     The  symbols  are  +  (a  :  b  :  c)  or  {111} 
and  {111}.     Two  unit  hemi-bipyramids  occurring  simultaneously  con- 
stitute the  monoclinic  unit  bipyramid,  Figs.  252  and  253. 
1  Normal  group  of  Dana. 


74 


MINERALOGY 


Since  this  system  differs  essentially  from  the  orthorhombic  in  the 
obliquity  of  the  a  axis,  it  follows  that  modified,  clino,  and  ortho  hemi-bipyra- 
mids  are  also  possible.  They  possess  the  following  general  symbols: 

Modified  hemi-bipyramids, 

±(d  :b  :  me),  m>0<  »,  or  {hhl}  and  —  {hhl}. 
Clino  hemi-bipyramids, 

±(nd  :b  :  we),  n>l',  or  {hid}  and  —  {hkl}. 
Ortho  hemi-bipyramids, 

±(a'  :nb  :mc),  n>l;  or  {hkl}   and  --   {hkl}. 

Prisms. — As  was  the  case  in  the  orthorhombic  system,  page  67,  there 
are  also  three  types  of  prisms  possible  in  this  system,  namely,  unit, 
clino  and  orthoprisms.  These  forms  cut  the  a  and  b  axes  and  extend 
parallel  to  the  vertical  axis. 

The  general  symbols  are: 


Unit  prism, 
Clinoprism, 
Orthoprism, 


(d  :  6  :  ooc),  {110},  Figs.  254  and  255. 

(nd  :  6  :  oo  c) ,  j  hko } ;  n  >  1 . 
(d  :  nb  :  <x>c),  {kho};  n>l. 


FIG.  254. 


FIG.  255. 


Domes. — In  this  system  two  types  of  domes  are  also  possible,  namely, 
those  which  extend  parallel  to  the  d  and  6  axes,  respectively.  Those, 
which  are  parallel  to  d,  are  termed  clinodomes  and  consist  of  four  faces, 
Fig.  256.  The  general  symbols  are: 


me, 


ohl}. 


MONOCLINIC  SYSTEM 


75 


Since  the  a  axis  is  inclined  to  the  6,  it 
follows  that  the  domes  which  are  parallel  to 
the  b  axis  consist  of  but  two  faces.  Figure 
257  shows  such  faces  enclosing  the  positive 
angle  and  are  termed  the  positive  hemi-ortho- 
dome, whereas  in  258  the  negative  hemi- 
orthodome  is  represented.  It  is  evident  that 
the  faces  of  the  positive  form  are  always  the 
smaller.  Figure  259  shows  these  hemidomes 
in  combination.  Their  general  symbols  are : 

Positive  hemi-orthodome, 

(d  :  cob  :  me),  {hoi}. 

Negative  hemi-orthodome, 

(d  :  cob  :mc),  \hol}. 


FIG.  256. 


7f 


FIG.  257. 


FIG.  258. 


FIG.  259. 


Pinacoids. — There  are  three  types  of  pinacoids  possible  in  the  mono- 
clinic  system,  namely, 


- 


FIG.  260. 


FIG.  261. 


Basal pinacoid,  ( o° d  :  cob  :c),  J001 } . 
Clinopinacoid,  (cod  :b  :  ooc),  J010J. 
Orthopinacoid,  (d  '•  cob  : °° c) ,  { 100 } . 


76 


MINERALOGY 


These  are  forms  consisting  of  but  two  faces.  Figures  260  and  261 
show  a  combination  of  these  pinacoids. 

All  forms  of  the  monoclinic  system  are  open  forms  and,  hence,  every 
crystal  of  this  system  is  a  combination. 

A  summary  of  the  forms  of  this  class  is  given  as  follows : 


Symmetry 

Plane 

•  Axis 

Center 

1 

(a  and  c  axes) 

1 

(b  axis) 

1 

Forms 

Symbols 

Faces 

Weiss                    Miller 

Hemi-bipyramids 

Unit 

±(d:b:c) 

{111} 
{111} 

4 

Modified 

±(d:  b:  me) 

{hhl\ 
\hhl] 

Clino- 

±(nd:b:mt) 

\hkl\ 
{hkl\ 

Ortho- 

±(d:nb:mt) 

{khl} 
[kid] 

Prisms 

Unit 

d:  b:  <x>c 

{110} 

4 

Clino- 

nd:b:  &>& 

{hko} 

Ortho- 

d:  nb:  «><* 

{kho} 

Clinodome 

oo  d:  b:  m6 

[ohl] 

4 

Hemi-orthodomes 

Positive 

d:  c°b:mt 

[hd\ 

2 

Negative 

d  :  cob:  mt 

{hoi} 

Pinacoids 

Basal 

ooa:  <x>b:  6 

{001} 

2 

Clino- 

cod:  b:  c°6 

{010} 

Ortho- 

d:  °°6:  oo^ 

{100} 

MONOCLINIC  SYSTEM 


77 


Combinations. — The  following  models  show  some  combinations  of 
the  forms  of  this  class. 

Figure  262.     m=(a:b:  «c),  {110};6  =  (ooa:6:  ooc),  {010}  ;p  = 
(0:6  :c),  (111}.     Gypsum,  CaSO4.2H2O. 


FIG.  262. 


FIG.  263. 


FIG.  264. 


FIG.  265. 


Figures  263,  264,  and  265.  m  =  (a  :  b  :  ooc),  {1101;  b  =  _(°°a:  b  ' 
»c),  (010);  c  =  (ooa  :  006  :  c),  (OOlj;  y  =  (a  :  <*b  :  2c),  (2011;  re  = 
(a  :  006  :c),  {I0l};o  =  (a  :  6  :c),  {111};  2  =  (3a  :  6  :  «>c),  (1301.  Or- 
thoclase,  KAlSi308. 


FIG.  266. 


FIG.  267. 


FIG.  268. 


FIG.  269. 


Figures  266,  267,  and  268.  m  =  (a  :b  :  «c),  {110};  a  =  (a  :  <*>&  : 
ooc),  {100};  6  =  («a  :6  :  «c),  {010};  c  =  (<oa  :  006  :c),  {001};  p_= 
=  -(o:6:c),  {lll}j  »=  -(a:6:2c),  {221};  o  =  (a:6:2c),  (221}; 
d  =  (a  :  006  :c),  {101}  ;s  =  (a  :6  :c),  {111}.  Pyroxene. 

Figure  269.     m  =  (a  :  b  :  ooc),  {110};  6  =  (ooa  :b  :  »c),  {010} ;r  = 
( oo a  :  b  :  c) ,  {Oil}.     Amphibole. 


CHAPTER  VII 
TRICLINIC  SYSTEM1 

Crystallographic  Axes. — This  system  includes  all  crystals  which  can 
be  referred  to  three  unequal  axes  intersecting  each  other  at  oblique 
angles.  The  axes  are  designated  as  in  the  orthorhombic  system, 
namely,  a,  brachyaxis;  b,  macroaxis;  and  c,  vertical  axis.  From  this  it 
follows  that  one  axis  must  be  held  vertically,  a  second  is  directed  toward 
+1  the  observer,  and  then  the  third  is  inclined 

from  right  to  left  or  vice  versa.  Usually  the 
brachyaxis  is  the  shorter  of  the  two  lateral 
axes.  Figure  270  shows  an  axial  cross  of  the 
triclinic  system.  The  oblique  angles  between 
the  axes  are  indicated  as  follows:  b  A  c  =  a, 
A  c  =  /3,  and  a  'A  5  =  7.  The  elements  of 
crystallization  consist  of  the  axial  ratio  and 
the  three  angles  a,  0,  and  7,  page  6. 

Classes  of  Symmetry. — There  are  but  two 
-c  classes  of  symmetry  in  the  triclinic  system, 

namely: 

1.  Pinacoidal  class. 

2.  Asymmetric  class. 

The  first  is  the  important  class. 

PINACOIDAL  CLASS2 

Symmetry. — A  center  of  symmetry  is  the  only  element  present. 
Hence,  forms  can  consist  of  but  two  faces,  namely,  face  and  parallel 
counter-face.  This  is  represented  diagrammatic-  ^"T\ 

ally  by  Fig.  271,  which  shows  a  triclinic  combi-  <•"""          I     x 
nation  projected  upon  the  plane  of  the  d  and  b      \  "^^  !       ^ 
axes.  \      i  ^^^\ 

Tetra-bipyramids. — As  already  shown,  triclinic  \  j       ^^^ 

forms  consist  of  but  two  faces.     Therefore,  since 
the  planes  of  the  Crystallographic  axes  divide  space 

into  four  pairs  of  dissimilar  octants,  it  follows  that  four  types  of 
pyramidal  forms  must  result.  These  are  spoken  of  as  tetrabipyramids. 
There  are,  hence,  four  tetra-bipyramids,  each  cutting  the  axes  at  their 
unit  lengths.  The  same  is  also  true  of  the  modified  brachy-  and 

1  Also  termed  the  anorthic,  asymmetric  or  clinorhomboidal  system. 

2  Normal  group  of  Dana. 

78 


TRICLINIC  SYSTEM 


79 


macro-bipyramids.  That  is  to  say,  the  various  bipyramids  of  the 
orthorhombic  system,  on  account  of  the  obliquity  of  the  three  axes, 
now  yield  four  tetra-bipyramids  each.  They  are  designated  as  upper 
right,  upper  left,  lower  right,  and  lower  left  forms,  depending  upon  which 
of  the  front  octants  the  form  encloses.  The  general  symbols  for  all 


FIG.   273. 

types  are  given  in  the  tabulation  on  page  80.  Figure  272  shows  the 
four  unit  tetra-bipyramids  in  combination. 

Hemiprisms. — Obviously  the  prisms  are  now  to  be  designated  as 
right  and  left  forms.  These  two  forms  are  in  combination  with  the  basal 
pinacoid  in  Fig.  273. 

Hemidomes. — All  domes  now  consist  of  but  two  faces.  Hence, 
we  may  speak  of  right  and  left  hemi-br  achy  domes,  and  upper  and  lower 
hemi-macrodomes.  These  forms  are  shown  in  combination  with  the  macro- 
and  brachypinacoids,  respectively,  in  Figs.  274  and  275. 


FIG.  274. 


FIG.  275. 


FIG.  276. 


Pinacoids. — These  forms  occur  with  their  usual  number  of  faces  and 
are  designated,  as  heretofore,  by  the  terms  basal,  brachy-,  and  macro- 


80 


MINERALOGY 


pinacoids,  depending  upon  the  fact  whether  they  intersect  the  c,  b,  or  a 
axes.     Figure  276  shows  these  pinacoids  in  combination. 

Summary. — The  various  forms  and  symbols  are  given  in  the  following 
table: 


Symmetry 

The    only   element  of  symmetry   in  this 
class  is  the  center  of  symmetry 

Forms 

All  forms  consist  of  two  faces 

Symbols 

Weiss 

Miller 

Unit 

&:   b:   6 
d:-b:    6 
a:   b:~c 
d:-b:-c 

{111} 
{111} 
{111} 
{111} 

Modified 

a:    b:    me 
d:-b:    me 
d:   b:  —me 
a:  -b:  —me 

{hhl} 
{hhl} 
{hhl} 
{hhl} 

Brachy 

* 

Macro 

nd:    b:    me 
nd:-b:    me 
nd:    b:  —me 
nd:-b:  -me 

{hkl} 
{hkl} 
{hkl} 
{hkl} 

d:    nb:    me 
a  :  -nb  :    me 
d:    nb:  —me 
d  :  —nb  :  —me 

{khl} 
{khl} 
{khl} 
{khl} 

Unit 

{            a:    b:  *?6 
\            d:-b:°°c 

{110} 
{110} 

Hemiprisms 
Brachy 

|           nd:    b:  coc 

(            nd  :  -b:  co  c 

{hko} 
{hko} 

Macro 

Id:    nb:  &>6 
d  :  —nb  :  °o  c 

{kho} 
{kho} 

Brachy 

I           cod:   b:  tn6 

\            co  d  :  —b  :  me 

[ohl] 
{ohl} 

Macro 

Id:  cob:    me 
d:  cob:  -me 

{hoi} 
{hoi} 

Basal 
Pinacoids                                                   Brachy 
Macro 

cod:  cob:c 

{001} 

^   ~       i 

co  ((  ;  o  ;  co  (; 

{010} 

d:  cob:  cofi 

f  Uoo} 

TRICLINIC  SYSTEM 


81 


Combinations.— Figure  277.    x  =  (a  :  b  :  c),(lllj; ;  r  =  (a  :  -  b  :  c), 
=(a:&:  a>c),{HO};M  =  (a:-b:  ooC),  {110} ;  s  =(o  :oo  6  :  2c), 
{201   ;  a  =  (a  :  c°&  :  coC),  {100}/  Axinite,  HCasAl2BSi4Oi6. 


FIG.  277. 


FIG.  278. 


FIG.  279. 


Figures  278  and  279.  m  =  (a  :  b  :  »c),  {110};  M  =  (a  :  -  b  :  «c), 
6  =  (ooa  :6  :  a>c),  {010}  ;c=  (°°a  :  «6  :c),  {001};a  =  (a  :  <»?>  :- 
-c),  {101}  ;o  =  a:b:-c  {111}  ;y  =  (a:  <»&  :  -2c),  {201}  ;n=  («_a  : 
-6:2c),{021};  /  =  (3a  :6  :  «c),  {130};  z  =  (3a  :  -  6  :  »c),  U30) 
Albite,  NaAlSi308. 


CHAPTER  VIII 
COMPOUND  CRYSTALS 

General  Statement. — The  crystals  considered  thus  far  have  been 
bounded  by  either  a  single  form  as  in  the  case  of  an  octahedron  (Fig.  57) 
or  by  a  combination  of  forms  (Fig.  78).  They  have,  however,  in  all 
cases  been  single  individuals.  In  many  instances,  crystals  occur  in 


FIG.  280. — Aggregate  of  crystals,  calcite.     Cumberland,  England. 

groups  and  may  be  designated  as  crystal  aggregates  or  parallel  groups.  A 
single  crystal  is  sometimes  made  up  of  two  or  more  individuals  arranged 
according  to  some  definite  law.  These  crystals  are  designated  as  twin 
crystals  or  simply  twins. 

Crystal  Aggregates. — These  are  groups  of 
crystals  arranged  in  no  definite  manner.  They 
are  usually  singly  terminated  (Figs.  280  and 
Figs.  427,  and  474,  pages  204  and  222): 

Parallel  Groups — Oftentimes  two  or  more 
crystals  of  the  same  substance  are  observed  to 
have  so  intergrown  that  the  crystallographic  axes 
of  the  one  individual  are  parallel  to  those  of  the 
others.  Such  an  arrangement  of  crystals  is 
termed  a  parallel  group.  Figures  281,  282  and 
283  show  such  groups  of  quartz  and  calcite,  respectively.  Occasionally, 
crystals  of  different  substances  are  grouped  in  this  way. 

Twin  Crystals. — Two  crystals  may  also  intergrow  so  that,  even  though 
parallelism  of  the  crystals  is  wanting,  the  growth  has,  nevertheless,  taken 

82 


FIG.  281. 


COMPOUND  CRYSTALS 


83 


place  in  some  definite  manner.  Such  crystals  are  spoken  of  as  twin  crys- 
tals, or  in  short,  twins.  Figure  284  illustrates  a  twin  crystal  com- 
monly observed  on  staurolite.  In  twin  crystals  both  individuals  have 
at  least  one  crystal  plane  or  a  direction  in  common.  Figure  285  shows 
a  twinned  octahedron.  The  plane  common  to  both  parts  is  termed  the 
composition  plane.  In  general,  the  plane  to  which  the  twin  crystal  is 
symmetrical  is  the  twinning  plane.  In  some  instances,  composition  and 


FIG.  282. — Parallel  group  of  quartz 
crystals.     Quindel,  Switzerland. 


FIG.  283. 


twinning  planes  coincide.  Both,  however,  are  parallel  to  some  possible 
face  of  the  crystal,  which  is  not  parallel  to  a  plane  of  symmetry.  The 
line  or  direction  perpendicular  to  the  twinning  plane  is  the  twinning 
axis.  A  twinning  law  is  expressed  by  indicating  the  twinning  plane  or 
axis. 

Twin  crystals  are  commonly  divided  into  two  classes:  (1)  Contact  or 
Juxtaposition  twins,  and  (2)  Penetration  twins.1     These  are  illustrated  by 


FIG.  284. 


FIG.  285. 


Figs.  285  and  284,  respectively.  Contact  twins  consist  of  two  indi- 
viduals so  placed  that  if  one  be  rotated  through  180°  about  the  twinning 
axis  the  simple  crystal  results.  In  penetration  twins  two  individuals 
have  interpenetrated  one  another.  If  one  of  the  individuals  be  rotated 


1  Also  designated  as  reflection  and  rotation  twins,  because  they  are  symmetrical  to 
a  plane  or  an  axis,  respectively. 


84 


MINERALOGY 


through  180°  about  the  twinning  axis  both  individuals  will  occupy  the 
same  position. 

Contact  and  penetration  twins  are  comparatively  common  in  all 
systems.  In  studying  twins,  it  must  be  borne  in  mind,  as  pointed  out 
on  page  12,  that  owing  to  distortion  the  two  individuals  may  not  be 
morphologically  symmetrical.  Re-entrant  angles  are  commonly  indica- 
tive of  twinning. 


FIG.  286. 


FIG.  287. 


Common  Twinning  Laws. — Cubic  System.  The  most  common  law 
in  the  cubic  system  is  known  as  the  spinel  law,  the  twinning  plane  being 
parallel  to  a  face  of  an  octahedron,  (a  :a  :a)  {HI}.  Figure  285  shows 
such  a  twin  crystal  of  the  mineral  spinel.  A  penetration  twin  of  fluorite 
is  shown  in  Fig.  286.  Here,  two  cubes  interpenetrate  according  to  the 
above  law. 

Figure  287  shows  a  penetration  twin  of  two  pyritohedrons  of  the 
mineral  pyrite.  These  twins  are  often  known  as  crystals  of  the  iron 
cross.  A  plane  parallel  to  a  face  of  the  rhombic  dodecahedron,  (a  :a  : 
oo a),  {110},  is  the  twinning  plane. 

Hexagonal  System. — Calcite  and  quartz  are  the  only  common 
minerals  belonging  to  this  system  which  furnish  good  examples  of 
twinning. 


FIG.  288. 


FIG.  289. 


FIG.  290. 


Upon    calcite    the  basal    pinacoid,    (oo«  :  «>«  :  eoa  :  c),    {0001},   is 
commonly  a  twinning  plane.     Figures  288  and  289  illustrate  this  law.1    A 

1  Compare  with  figures  139  and  144. 


COMPOUND  CRYSTALS 


85 


plane  parallel  to  a  face  of  the  negative  rhombohedron,  —  (ooa  :  2a  : 
2a  :  c),  {0112},  may  also  be  a  twinning  plane  as  illustrated  by  Fig.  290. 
These  are  the  most  common  laws  on  calcite. 


FIG.  291. 


FIG.  292. 


The  common  or  Dauphine  twinning  law  on  quartz  is  shown  in  Fig. 
291.  Here  either  two  right-  or  two  left-hand  crystals  interpenetrate, 
after  one  has  been  revolved  180°  about  the  c  axis  as  the  twinning  axis. 

The  so-called  Brazilian  law  is  common  on  twins 
of  quartz,  Fig.  292.  Here,  right  and  left  crystals  have 
interpenetrated  so  that  the  twin  is  now  symmetrical 
to  a  plane  parallel  to  a  face  of  the  prism  of  the  second 
order,  (2a  :  2a  :  a  :  «>c),  {1120}. 

Tetragonal  System. — Most  of  the  twin  crystals  of 
this  system  are  to  be  observed  on  substances  crystal- 
lizing in  the  ditetragonal  bipyramidal  class.  A  plane 
parallel  to  a  face  of  the  unit  bipyramid  of  the  second 
order,  (ooa  :  a  :  c)  {Oil},  commonly  acts  as  the  twinning  plane.  Figure 
293  shows  crystals  of  cassiterite  twinned  according  to  this  law. 

Orthorhombic  System. — The  most  common  twins  of  this  system 
belong  to  the  bipyramidal  class  in  which  any  face  aside  from  the  pina- 


FIG.  293. 


FIG.  294. 


FIG.  295. 


FIG.  296. 


coids  may  act  as  twinning  plane.  Figure  294  shows  a  penetration 
twin  of  staurolite,  where  the  brachydome,  (°°a  :  b  :  %c),  {032}, 
acts  as  the  twinning  plane.  Figure  295  shows  the  same  mineral  with 
the  bipyramid,  (%a  :  b  :  %c),  {232},  as  the  twinning  plane.  Figure  296 


86 


MINERALOGY 


represents  a  contact  twin  of  aragonite.     Here  the  unit  prism,  (a  :b  :  «c), 
{110},  is  the  twinning  plane. 

Monoclinic  System. — In  this  system,  gypsum  and  orthoclase  furnish 
some  of  the  best  examples.     Figure  297  shows  a  contact  twin  of  gypsum 


FIG.  297. 


FIG.  298. 


FIG.  299. 


in  which  the  orthopinacoicf,  (a  :  °°6  :'°°c),  {100},  is  the  twinning  plane. 
Penetration  twins  of  orthoclase  are  shown  in  Figs.  298  (left)  and  299 
(right).  Here,  the  c  axis  acts  as  twinning  axis.  This  is  known  as  the 


FIG.  300. 


FIG.  301. 


Karlsbad  law  on  orthoclase.  Two  other  twinning  laws  are  also  fre- 
quently observed  on  orthoclase,  namely,  the  Baveno  and  Mannebach 
laws,  where  the  clinodome  (°°a  :  b  :  2c),{021j  (Fig.  300),  and  the  basal 


FIG.  302. 


FIG.  303. 


pinacoid(ooa  :  cob  :c),  {001}  (Fig.  301), respectively, act  as  the  twinning 
planes. 

Triclinic  System. — Since  there  are  no  planes  of  symmetry  in  this 
system,  any  plane  may  act  as  the  twinning  plane.     The  mineral  albite 


COMPOUND  CRYSTALS 


87 


furnishes  good  examples.  In  Fig.  302,  the  brachypinacoid,  ( c°  a  :b  : 
oo c),  (010),  is  the  twinning  plane.  This  is  the  albite  law.  Another 
common  law  is  shown  by  Fig.  303.  Here,  the  basal  pinacoids  of  both 
individuals  are  parallel,  the  crystallographic  6  axis  acting  as  the  twinning 
axis.  This  is  known  as  the  pericline  law. 

Repeated  Twinning. — In  the  foregoing,  crystals  consisting  of  but 
two  individuals  have  been  discussed.  Intergrowths  of  three,  four, 
five  or  more,  individuals  are  termed  threelings,  fourlings,  fivelings,  and  so 


FIG.  304. 


FIG.  305. 


FIG.  306. 


on.  Polysynthetic  and  cyclic  twins  are  the  result  of  repeated  twinning. 
In  the  polysynthetic  twins  the  twinning  planes  between  any  two  individuals 
are  parallel.  This  is  illustrated  by  Figs.  304  and  305  showing  poly- 
synthetic twins  of  albite  and  aragonite,  respectively.1  If  the  individuals 
are  very  thin  the  re-entrant  angles  are  usually  indicated  by  striations. 
Cyclic  twins  result  when  the  twinning  planes  do  not  remain  parallel, 
as  for  example  when  adjacent  or  opposite  faces  of  a  form  act  as  twinning 
planes.  This  is  shown  by  the  cyclic  twins  of  rutile,  Fig.  306,  in  which 
adjacent  faces  of  the  unit  bipyramid  of  the  second  order  (<x>a  :a  :c), 
{Oil }  act  as  twinning  planes. 

Mimicry. — As  a  result  of  repeated  twinning,  forms  of  an  apparently 
higher  grade  of  symmetry  often  result.     This  is  especially  true  of  those 


//6V 


FIG.  307. 


FIG.  308. 


substances   possessing   pseudosymmetry,    page   56.     Figure  307  shows 
a  trilling  of  the  orthorhombic  mineral  aragonite,  CaCO3,  which  is  now 
apparently  hexagonal   in   its  outline.     In  Fig.  308  the  cross-section  is 
shown.     This  phenomenon  is  called  mimicry. 
1  Compare  with  figures  302  and  296. 


CHAPTER  IX 
PHYSICAL  PROPERTIES 

Those  physical  properties  which  are  easily  recognized  or  determined, 
and  are  important  in  the  rapid  determination  of  minerals  will  be  dis- 
cussed in  this  chapter.  The  optical  properties  involving  the  use  of  the 
microscope  will  be  treated  later. 

Luster. — -The  luster  of  a  mineral  is  the  appearance  of  its  surface  in 
reflected  light,  and  is  a  property  of  fundamental  importance  in  the 
recognition  of  minerals.  Lusters  may  be  divided  into  two  large  groups, 
namely,  metallic  and  non-metallic.  Metallic  luster  is  indicative  of  metals 
and  is  exhibited  by  minerals  which  are  opaque  or  nearly  so,  and  quite 
heavy.  All  other  lusters  may  be  designated  as  non-metallic,  some  of  the 
more  important  being: 

Vitreous.  —The  luster  of  glass  or  quartz. 

Adamantine. — The  exceedingly  brilliant  luster  of  minerals  with  high 
indices  of  refraction,  as  the  diamond  and  pyromorphite. 

Resinous. — -The  luster  or  appearance  of  resin.  This  is  well  shown 
by  sphalerite. 

Greasy. — >The  appearance  of  an  oiled  surface.    Example,    nephelite. 

Pearly. — -This  is  similar  to  the  luster  of  the  mother  of  pearl.  It  is 
commonly  shown  by  minerals  with  a  lamellar  or  platy  structure,  and 
by  those  with  pronounced  cleavages.  Example,  talc. 

Silky. — This  luster  is  the  result  of  a  fibrous  structure  and  is  well  shown 
by  fibrous  gypsum  (satin  spar)  and  asbestos. 

Dull. — -Not  bright  or  shiny,  good  examples  being  chalk  and  kaolin. 
Sometimes  called  earthy  luster. 

The  terms  splendent,  shining,  glistening,  and  glimmering  are  sometimes 
used.  They  have  reference  to  the  intensity  or  quantity  of  light  reflected. 
In  some  instances  luster  is  not  the  same  on  all  faces  of  a  crystal.  Thus, 
on  apophyllite  it  is  pearly  on  the  basal  pinacoid  and  vitreous  elsewhere. 
When  a  luster  is  intermediate  between  metallic  and  non-metallic  it  is 
frequently  called  submetallic. 

Color. — The  color  of  a  mineral  is  one  of  the  first  physical  properties  to 
be  observed.  Some  minerals  have  a  fairly  constant  color  and  are  called 
idiochromatic.  Thus,  sulphur  is  always  yellow  and  malachite  green.  In 
other  minerals  the  color  may  vary  greatly,  due  to  the  presence  of  pig- 
ments, inclusions,  or  other  impurities.  Such  minerals  are  termed  allo- 
chromatic.  Good  examples  are  calcite  and  quartz,  both  of  which  show 

88 


PHYSICAL  PROPERTIES  89 

a  great  variety  of  colors.  The  terms  used  in  describing  the  various 
colors  need  no  explanation. 

Play  or  Change  of  Colors.  —Some  minerals  exhibit  different  colors  as 
the  specimen  is  slowly  turned,  or  as  the  direction  of  observation  is  changed. 
This  is  well  illustrated  by  labradorite  and  opal. 

Opalescence.  —This  consists  of  milky  or  pearly  reflections  from  the 
interior  of  the  specimen,  as  is  frequently  seen  in  opal  and  moonstone. 
Opalescence  is  usually  observed  to  best  advantage  on  specimens  with 
rounded  and  polished  surfaces. 

Iridescence.  —Some  minerals  show  a  play  of  bright  colors  due  to  a  thin 
coating  or  film  on  the  surface  of  the  specimen,  as  is  often  the  case  with 
limonite.  In  some  cases  it  is  due  to  cleavage  cracks. 

Tarnish. — After  certain  minerals  have  been  exposed  to  air,  the  color 
of  the  exposed  portions  differs  distinctly  from  that  of  the  freshly  frac- 
tured surfaces.  Example,  bornite. 


FIG.  309. — Asterism  shown  by  museovite  from  South  Burgess,  Canada.  * 

Asterism. — Some  minerals,  like  certain  sapphires  and  rubies,  exhibit 
a  starlike  light  effect  when  viewed  in  reflected  light.  Other  minerals 
show  a  similar  effect  in  transmitted  light,  that  is,  when  a  source  of 
light  is  viewed  by  holding  the  specimen  close  to  the  eye,  for  example, 
museovite  (Fig.  309). 

Streak. — 'This  is  the  color  of  the  fine  powder  of  a  mineral  and  is  fre- 
quently made  use  of  in  the  determination  of  minerals.  Although  the 
color  of  minerals  may  vary  greatly  the  streak  is  often  fairly  constant. 
The  color  of  the  streak  may  be  determined  by  crushing,  filing,  or  scratch- 
ing. The  usual  and  most  satisfactory  method,  however,  is  to  rub  the 
mineral  on  a  piece  of  white,  unglazed  porcelain,  the  streak  plate.  The 
ease  or  difficulty  with  which  the  streak  is  obtained  is  to  some  extent  indi- 
cative of  the  hardness  of  a  mineral. 

*  Figs.  309,  346  to  348,  353  to  359  and  362  to  366  are  from  Hauswaldt's  Interferenzer- 
scheinungen  im  Polarisirten  Lichte. 


90 


MINERALOGY 


Some  minerals  having  the  same  color  possess  streaks  which  differ 
materially.  Thus,  the  following  three  iron  minerals  are  all  black,  but 
they  can  be  readily  distinguished  by  their  streaks:  hematite,  red  brown 
streak;  limonite,  yellow  brown  streak;  magnetite,  black  streak. 

Hardness. — The  resistance  offered  by  a  mineral  to  abrasion  or  scratch- 
ing is  termed  hardness.  It  is  indicated  relatively  in  terms  of  Mohs's 
scale,  which  consists  of  ten  common  minerals  arranged  in  order  of  in- 
creasing hardness,  as  follows: 


1.  Talc, 

2.  Gypsum, 

3.  Calcite, 

4.  Fluorite, 

5.  Apatite, 


6.  Feldspar, 

7.  Quartz, 

8.  Topaz, 

9.  Corundum, 
10.  Diamond. 


Beryl,  7.5  to  8  in  hardness,  is  often  substituted  for  topaz  in  the  above 
scale. 

Substances,  scratched  by  and  which  in  turn  scratch  some  one  member 
of  the  scale,  are  said  to  have  the  hardness  assigned  to  that  member.  In 
determining  the  hardness  of  a  mineral  the  scratch 
made  should  be  as  short  as  possible,  not  over  J^ 
inch,  and  care  exercised  to  distinguish  between 
a  scratch  and  a  chalk  mark.  The  latter  is  easily 
removed  by  rubbing. 

The  determination  of  the  approximate  hard- 
ness is  greatly  simplified  by  using  the  finger  nail, 
copper  coin,  the  knife  blade,  or  a  piece  of  window 
glass  which  possess  the  following  values: 

Finger  nail,  up  to  2.5 
Copper  coin,  up  to  3 
Knife  blade,  up  to  5.5 
Window  glass,  5.5 


FI.G.  310.  — Albin 
Weisbach  (1833-1901). 
Professor  of  mineralogy 
in  the  Saxon  School  of 
Mines,  Freiberg,  Ger- 
many. Pioneer  in  the  use 
of  physical  properties  for 
the  determination  of 
minerals. 


Since  the  majority  of  the  minerals  are  less  than 
6  in  hardness,  this  simplified  scale  is  of  great  con- 
venience in  determining  the  approximate  hard- 
ness in  the  laboratory  and  field. 

In  the  tables  for  the  determination  of  minerals,  which  follow  on  pages 
380  to  547,  minerals  have  been  divided  into  three  groups  based  upon  the 
hardness  of  calcite  and  feldspar,  thus:  (1)  1  to  3,  softer  than  or  as  hard  as 
calcite;  (2)  3  to  6,  harder  than  calcite  but  not  harder  than  feldspar;  (3) 
over  6,  harder  than  feldspar. 

Specific  Gravity. — The  specific  gravity  of  a  solid  substance  is  its  weight 
compared  with  the  weight  of  an  equal  volume  of  water.  The  specific 
gravity  of  a  mineral  is  constant,  provided  its  composition  does  not  vary. 


PHYSICAL  PROPERTIES 


91 


Many  minerals  with  strikingly  similar  physical  properties  often  possess 
specific  gravities  which  differ  materially.  Thus,  celestite,  SrSO4,  with 
a  specific  gravity  of  3.95  can  be  easily  distinguished  from  barite,  BaSO4, 
having  a  specific  gravity  of  4.5. 

The  specific  gravity  of  minerals  can  be  determined  most  conveniently 
by  means  of  the  recording  Jolly  balance,1  see  Fig.  311.  This  balance 
consists  of  a  rectangular  upright  tube  to  which  the  inner  fixed  vernier 
and  the  movable  doubly  graduated  scale  are  attached.  This  tube  contains 
a  round  tube  which  can  be  moved  by  the  large  milled-head.  To  this 
second  tube  the  outer  movable  vernier  is  fastened.  A  movement  of 


'W 


-  6  - 

-  r 


FIG.  311, 


FIG.  312. 


the  round  tube  upward  carries  the  second  vernier  and  the  graduated 
scale  with  it.  Within  the  round  tube  there  is  a  rod  of  adjustable  length, 
which  carries  the  spiral  spring,  index,  and  scale  pans.  With  this  form 
of  balance  only  two  readings  and  a  simple  division  are  necessary  to  de- 
termine the  specific  gravity. 

In  using  the  balance  it  is  necessary  that  the  graduated  scale,  the  two 
verniers,  and  the  index,  which  is  attached  to  the  spiral  spring,  all  be  at 
zero,  the  lower  scale  pan  being  immersed  in  water.  This  is  accomplished 
by  adjusting  approximately  by  hand  the  length  of  the  rod  carrying  the 
spring  and  then  introducing  the  necessary  correction  by  means  of  the 
micrometer  screw  shown  directly  below  the  spring  in  the  cut,  Fig.  311 

1  This  balance  is  manufactured  by  Eberbach  and  Son  Company,  Ann  Arbor, 
Michigan. 


92  MINERALOGY 

A  fragment  is  then  placed  on  the  upper  scale  pan  and  by  turning  the  large 
milled-head  the  round  tube,  graduated  scale,  and  outer  vernier  are  all 
driven  upward  until  the  index  on  the  spring  is  again  at  zero.  The  fixed 
inner  vernier  W,  Fig.  312  now  records  the  elongation  of  the  spring  due 
to  the  weight  of  the  fragment  in  the  air.  The  scale  is  then  clamped  by 
means  of  the  screw  at  the  lower  end  of  it,  Fig.  311.  The  fragment  is  now 
transferred  to  the  lower  scale  pan,  immersed  in  water,  and  the  round  tube 
lowered  by  the  large  milled-head  until  the  index  again  reads  at  zero. 
During  this  operation  the  outer  vernier  moves  downward  on  the  gradu- 
ated scale  and  its  position  may  now  be  indicated  by  L,  Fig.  312.  This  is 
obviously  the  decrease  in  the  elongation  of  spring  due  to  the  immersion 
of  the  fragment  in  water.  The  readings  at  W  and  L  are  all  the  data  nec- 
essary for  the  calculation  of  the  specific  gravity.  For 

Weight  in  air  W 

Specific  gravity  =  j- .        .  ,     . j-  =  -y- 

Loss  oj  weight  in  water       L 

It  is  also  obvious  that  these  readings  are  recorded  so  that  they  may  be 
checked,  if  necessary,  after  the  operations  and  calculation  are  completed. 
By  means  of  this  balance  specific  gravity  determinations 
can  be  readily  made  in  about  two  minutes,  using  for  the 
purpose  a  crystal  or  larger  mineral  fragment  as  free  from 
impurities  as  possible.     In  order  to  determine  the  specific 
gravity  of  minerals  in  smaller  fragments  or  grains  it  is  nec- 
essary to  make  use  of  the  pycnometer  or  specific  gravity 
flask. 

The  pycnometer  in  its  simplest  form  consists  of  a  small 
glass  flask  (Fig.  313)  fitted  with  a  ground  glass  stopper, 
which  is  pierced  length-wise  by  a  capillary  opening.  The 
FIG  3i3  pycnometer  is  first  weighed  empty  (A),  and  when  filled  with 
distilled  water  (B).  The  pj^cnometer  is  then  emptied 
and  after  being  thoroughly  dried,  the  mineral  powder,  fragments,  or 
grains  are  introduced  and  the  whole  weighed  (C).  The  pycnometer  is 
again  filled  with  water  and  a  fourth  weighing  made  (D).  The  specific 
gravity  can  then  be  determined  as  follows: 

C  -  A 


Specific  gravity 


B  +  C -  A  - D 


Care  must  be  exercised  to  remove  all  the  air  bubbles  which  can  usually 
be  done  by  boiling  the  water  and  then  allowing  it  to  cool.  When  this 
method  is  carefully  carried  out,  very  accurate  results  may  be  obtained. 
When  substances  are  soluble  in  water,  the  determination  may  be  made  by 
using  some  liquid  in  which  they  are  insoluble,  for  example  alcohol,  and 
then  multiplying  the  result  by  the  specific  gravity  of  the  liquid  employed. 

The  chemical  balance  and  also  certain  heavy  liquids  in  connection 


PHYSICAL  PROPERTIES  93 

with  the  Westphal  balance  are  sometimes  used  for  the  determination  of 
specific  gravity.  These  methods  are  very  accurate  but  time  consuming. 
They  are  generally  employed  iir  mineralogical  research  and  but  rarely 
by  students  of  elementary  mineralogy. 

Magnetism. — Comparatively  strong  magnetism  is  shown  by  a  few 
iron-bearing  minerals,  their  powders  or  small  fragments  being  readily 
attracted  by  a  magnet.  A  convenient  method  to  test  the  presence  or 
absence  of  magnetism  in  a  mineral,  without  crushing  it,  is  to  suspend  a 
small  horseshoe  magnet  from  the  finger  so  that  it  may  swing  freely  and 
then  bring  the  specimen  under  consideration  close  to  the  magnet.  If  the 
specimen  is  magnetic  the  magnet  will  be  deviated  from  its  vertical  posi- 
tion, the  amount  of  the  deviation  indicating  roughly  the  relative  strength 
of  the  magnetism.  Examples,  magnetite  and  pyrrhotite.  Some  min- 
erals even  act  as  natural  magnets  or  lodestones  and  will  attract  consider- 
able quantities  of  iron  filings,  tacks,  and  nails.  Examples,  certain 
varieties  of  magnetite,  see  Fig.  563,  page  269. 


FIG.    314.— Cubical  FIG.    315.— Octahedral  cleav- 

cleavage,  halite.    Stass-  age,     fluorite.      Near    Rosiclare, 

furt,  Germany.  Illinois. 

Cleavage. — Many  minerals  split  or  separate  easily  along  definite 
planes.  This  property  is  called  cleavage  and  is  frequently  very  con- 
spicuous and  highly  characteristic.  A  mineral  can  be  cleaved  by  either 
striking  it  a  properly  directed  blow  with  a  hammer  or  by  pressing  upon 
it  in  a  definite  direction  with  the  sharp  edge  of  a  knife  blade.  The  planes 
along  which  the  separation  takes  place  are  called  cleavage  planes.  These 
planes  are  parallel  to  possible  crystal  faces  and  are  so  designated.  Thus, 
cubical  cleavage,  that  is  parallel  to  the  faces  of  the  cube,  is  shown  by 
galena  and  halite  (Fig  314);  octahedral  cleavage  by  the  diamond  and 
fluorite  (Fig.  315);  rhombic  dodecahedral  cleavage  by  sphalerite;  rhom- 
bohedral  cleavage  by  calcite;  prismatic  cleavage  by  barite  and  celestite; 
basal  cleavage  by  topaz  and  mica;  clinopinacoidal  cleavage  by  gypsum. 
The  manner  and  ease  with  which  cleavages  are  obtained  are  indicated 
by  such  terms  as  perfect,  imperfect,  distinct,  easy,  and  so  forth.  Thus, 
calcite  is  said  to  have  a  perfect  rhombohedral  cleavage. 


94  MINERALOGY 

The  cleavage  of  minerals,  and  especially  of  crystals,  can  often  be 
recognized  by  the  presence  of  cleavage  cracks.  In  such  cases  it  is  not 
necessary  to  resort  to  striking  the  specimen  a  blow  and,  hence,  shattering 
it  somewhat,  or  to  the  use  of  a  knife  edge.  As  cleavage  is  dependent  upon 
regularity  of  structure,  it  is  only  observed  on  crystallized  substances. 
Amorphous  substances  do  not  possess  cleavage. 

Parting  is  a  separation  somewhat  similar  to  cleavage  and  is  sometimes 
called  false  cleavage.  It  is  frequently  the  result  of  polysynthetic  twin- 
ning. It  may  also  be  due  to  pressure  applied  in  definite  directions. 

Fracture. — The  fracture  of  a  mineral  refers  to  the  character  of  the 
surface  obtained  when  crystalline  substances  are  broken  in  directions 
other  than  those  along  which  cleavage  or  parting  may  take  place.  Min- 
erals with  no  cleavage  or  with  only  a  poor  cleavage  yield  fracture  sur- 
faces very  easily.  As  amorphous  substances  are  devoid  of  cleavage,  they 
always  show  fracture  surfaces  when  shattered  by  a  blow.  The  following 
types  of  fracture  may  be  distinguished. 

Conchoidal. — The  surfaces  are  curved  and  shell-like  in  character. 
Example,  quartz. 

Even. — The  fracture  surfaces  are  flat  or  nearly  so,  that  is,  they  are 
approximately  even  planes.  Example,  lithographic  limestone. 

Uneven. — The  surfaces  are  more  uneven.     Example,  rhodonite. 

Hackly. — The  fracture  surfaces  have  many  sharp  points,  and  are 
rough  and  irregular.  Example,  copper. 

Splintery. — The  mineral  breaks  into  splinters  or  fibers.  Example, 
pectolite. 

Earthy. — The  irregular  fracture  characteristic  of  earthy  substances 
like  chalk,  kaolin,  and  bauxite. 

Tenacity. — Under  this  heading  is  included  the  behavior  of  minerals 
when  an  attempt  is  made  to  break,  cut,  hammer,  crush,  bend,  or  tear 
them.  The  most  important  kinds  of  tenacity  are  the  following: 

Brittle. — Easily  broken  or  powdered,  and  cannot  be  cut  into  slices. 
Example,  quartz. 

Sectile. — Can  be  cut  and  yields  shavings,  which  crumble  when  struck 
with  a  hammer,  Example,  gypsum. 

Malleable. — Can  be  hammered  out  into  thin  sheets.  Examples, 
gold  and  copper. 

Ductile. — Can  be  easily  drawn  into  wire.  Example,  copper  and 
silver. 

Flexible. — Thin  layers  of  the  mineral  can  be  bent  without  breaking 
and  they  remain  bent  after  the  pressure  has  been  removed.  Example, 
foliated  talc. 

Elastic. — Thin  layers  of  the  mineral  may  be  bent  without  breaking 
but  they  resume  their  positions  when  the  pressure  is  removed.  Example, 
mica. 


PHYSICAL  PROPERTIES  95 

Transparency  or  Diaphaneity. — This  is  the  ability  of  a  mineral  to 
transmit  light.  This  property  can  usually  be  recognized  upon  first  sight, 
as  is  also  the  case  with  color  and  luster.  Substances  through  which 
objects  can  be  easily  and  distinctly  seen  are  said  to  be  transparent. 
Example,  colorless  quartz.  When  light  passes  through  the  substance  but 
objects  are  seen  only  indistinctly,  the  mineral  is  translucent.  Example, 
Mexican  onyx.  Substances  are  opaque  when  no  light  is  transmitted 
even  through  thin  edge  or  layers.  Example,  graphite.  Subtransparent 
and  subtranslucent  indicate  intermediate  stages. 

Taste. — Minerals  soluble  in  water  or  the  saliva  generally  possess  a 
characteristic  taste,  which  may  be  designated  as  follows: 

Add. — The  sour  taste  of  sulphuric  acid. 

Alkaline. — The  taste  of  soda  or  potash. 

Astringent. — This  causes  a  contraction  or  puckering.     Example,  alum. 

Bitter. — The  taste  of  epsom  or  bitter  salts. 

Cooling. — The  taste  of  potassium  or  sodium  nitrate. 

Metallic. — A  very  disagreeable  brassy  metallic  taste.  Example, 
decomposed  pyrite. 

Pungent. — A  sharp  and  biting  taste.     Example,  ammonium  chloride. 

Saline. — The  salty  taste  of  halite  or  sodium  chloride. 

Although  the  taste  of  a  mineral  is  not  a  property  of  great  importance, 
it  is  sometimes  very  useful  in  the  rapid  determination  of  minerals. 

Odor. — Some  minerals  give  off  characteristic  odors  when  breathed 
upon,  rubbed,  scratched,  pounded,  or  heated,  which  are  designated  as 
follows : 

Argillaceous. — The  clay-like  odor  obtained  by  breathing  upon  kaolin. 

Bituminous. — The  odor  produced  by  minerals  containing  bituminous 
or  organic  matter.  Usually  it  is  easily  obtained  by  striking  the  specimen 
with  a  hammer.  Example,  asphalt. 

Fetid. — The  odor  of  rotten  eggs,  due  to  a  liberation  of  hydrogen  sul- 
phide. Example,  barite. 

Garlic. — The  odor  of  the  vapors  evolved  when  arsenical  minerals  are 
heated.  Also  called  alliaceous  or  arsenical  odor.  Example,  arsenopyrite. 

Horse-radish. — The  very  disagreeable  odor  of  decaying  horse-radish 
obtained  by  heating  compounds  of  selenium. 

Sulphurous. — The  odor  of  sulphur  dioxide,  which  is  liberated  when 
sulphur  or  sulphides  are  heated  or  roasted.  Example,  pyrite. 

Feel  or  Touch. — The  impression  one  receives  by  handling  or  touching 
a  mineral  is  designated  as  its  feel  or  touch.  The  following  terms  are  in 
common  use. 

Cold. — The  feel  of  good  conductors  of  heat.  Examples,  metallic 
minerals  like  copper  and  silver,  and  gems . 

Greasy  or  Soapy. — The  slippery  feel  of  talc. 

Harsh  or  Meager. — Rough  to  the  touch.     Example,  chalk. 


96  MINERALOGY 

Smooth.  —  Without  projections  or  irregularities.  Example,  meer- 
schaum. 

Some  porous  minerals  like  chalk,  kaolin,  and  diatomaceous  earth 
adhere  readily  to  the  tongue. 

Structure.  —  Many  minerals  occur  frequently  in  good  crystals,  as  is 
the  case  with  calcite  and  quartz.  But  for  the  most  part  minerals  are 
found  in  masses  of  various  types,  which  may  be  either  crystalline  or  amor- 
phous in  character.  In  fact,  the  general  structure  of  minerals  may  be 
classified  as  follows: 

Crystals  —  Crystal    Aggre- 

1.  Crystalloids  —Crystalline  Structure  </  ExamPle' 


Irregular  —  Crystalline 

Grains  or  Par-     Aggregates.  Ex- 
ticles.  ample,  marble. 

2.  Colloids  and  Gels  —  Amorphous  Structure  —  Masses  —  Example,   opal 

The  term  crystalloid  refers  to  well  developed  isolated  crystals  or  to 
groups  or  aggregates  of  crystals  (Fig.  474,  page  222)  and  also  to  grains  or 
particles  possessing  crystal  structure,  but  devoid  of  natural  plane  sur- 
faces which  are  one  of  the  outward  expressions  of  crystallinity.  Masses 
of  grains  or  particles  are  called  crystalline  aggregates  (Fig.  516,  page 
245)  .  Colloids  or  gels  do  not  crystallize  and  therefore  yield  only  amor- 
phous masses,  which  are  without  any  definite  form.  Those  masses  which 
appear  to  the  unaided  eye  to  be  amorphous,  but  are  in  reality  crystalline, 
as  revealed  by  the  microscope,  are  called  cryptocrystalline. 

As  was  shown  in  Chapters  II  to  VIII,  crystals  occur  in  a  great 
diversity  of  form.  These  forms  are  very  useful  in  the  determination 
of  minerals.  There  are  also  many  types  of  crystalline  agrgegates  and 
amorphous  masses,  of  which  the  following  are  the  most  important. 

Acicular.  —  Composed  of  delicate  and  slender  needle-like  crystals 
(Fig.  666,  page  325). 

Amygdaloidal.  —  Almond  shaped  mineral  masses  occurring  in  small 
cavities  in  lavas  (Fig.  415,  page  197). 

Arborescent.  —  Branching  or  tree-like  aggregates  of  crystals  (Fig.  316). 

Bladed.  —  A  tabular  or  platy  structure,  the  individuals  resembling 
grass  or  knife  blades.  The  blades  may  be  parallel  or  divergent  (Fig.  583, 
page  282). 

Botyroidal.  —  Closely  united  spherical  masses,  resembling  a  bunch 
of  grapes  (Fig.  529,  page  253). 

Capillary.  —  Composed  of  exceedingly  slender  or  hair-like  crystals. 

Cellular.  —  Made   up   of   pores,  like  a   sponge.     Porous. 

Clastic.  —  Made  up  of  fragments. 

Columnar.  —  Composed  of  thick  fibers  or  columns,  often  parallelly 
grouped  (Fig.  556,  page  264). 


PHYSICAL  PROPERTIES 


97 


Concentric. — Spherical  layers  about  a  common  center,  similar  to 
the  layers  of  an  onion  (Fig.  477,  page  223). 

Concretionary. — Rounded  or  nodular  masses   (Fig.  481,  page  224). 

Dendritic. — Branching  and  fern-like  structure  (Fig.  317). 

Drusy.- — A  rough  surface  due  to  a  large  number  of  small  closely 
crowded  crystals  (Fig.  545,  page  260). 

Fibrous. — Consisting  of  slender  fibers  or  filaments  (Fig.  573,  page 
276). 

Filiform. — Composed  of  thin  wires,  often  twisted  or  bent  (Fig.  421, 
page  199). 

Foliated. — Made  up  of  plates  or  leaves  which  are  easily  separated. 

Globular. — Spherical,  or  nearly  so. 

Granular. — Composed  of  closely  packed  grains,  which  may  be  either 
coarse  or  fine  (Fig.  603,  page  289). 

Lamellar. — Made  of  thin  plates  or  layers. 

Lenticular. — Lens-shaped . 


FIG.  316. — Arborescent  copper. 
Phoenix  Mine,  Lake  Superior  Dis- 
trict. 


FIG.  317. — Dendritic  manga- 
nite  on  sandstone,  Malone,  New 
York. 


Mammillary. — Large  and  rounded,  larger  than  a  grape. 

Micaceous. — Composed  of  very  thin  plates  or  scales,  like  those  of 
mica. 

Nodular. — Rounded  masses  of  irregular  shape  (Fig.  481,  page  224). 

Oolitic. — Composed  of  small  rounded  particles  the  size  of  fish-eggs 
(Fig.  318). 

Phanerocrystalline. — Crystals  or  coarsely  crystalline  (Fig.  649, 
page  317). 

Pisolitic. — Composed  of  rounded  particles,  the  size  of  peas  or  buck- 
shot (Fig.  502,  page  235). 

Plumose. — Feathery  structure,  sometimes  observed  on  mica. 

Reniform. — Composed  of  large  rounded  masses  resembling  a  kidney 
in  shape  (Fig.  495,  page  230). 

Reticulated. — Composed  of  fibers  crossing  in  meshes  like  in  a  net. 
Fig.  319). 

Scaly. — Composed  of  small  thin  scales  or  plates. 

7 


98 


MINERALOGY 


Sheaf -like. — Aggregates  resembling  a  sheaf  of  wheat  in  outline 
(Fig.  673,  page  327). 

Stalactite. — Cylindrical  or  conical  masses  resembling  icicles.  (Fig. 
476,  page  222). 


FIG.  318. — Oolitic  limestone. 
Bedford,  Indiana. 


FIG.  319. — Reticulated  silver.     Silver  King 
Mine,   Arizona. 


Stellate. — Radiating    crystals    or    fibers    producing    star-like    forms. 

Tabular. — Composed  of  broad  flat  surfaces,  tablet-like  (Fig.  532, 
page  255). 

Less  frequently  used  terms  are  listed  in  the  glossary,-  page  366.  These 
are  employed  only  when  finer  distinctions  in  structure  are  made. 


CHAPTER  X 
THE  POLARIZING  MICROSCOPE 

Optical  Methods. — During  recent  years  great  advances  have  been 
made  in  perfecting  simple  methods  by  which  certain  optical  constants  of 
solids  may  be  easily  and  rapidly  determined.  Many  of  these  methods  in- 
volve the  use  of  the  mineralogical  or  polarizing  microscope,  which  differs 
materially  from  the  microscope  ordinarily  used  by  biologists,  pathologists, 
and  other  scientists,  in  that  it  is  equipped  with  a  rotating  stage,  and 
various  devices  permitting  the  study  of  objects  in  polarized  light.  In 
fact,  in  determining  solids  by  optical  methods  polarized  light  is  indis- 
pensible.  It  will  therefore  be  necessary  to  review  briefly  some  of  the 
essential  properties  of  light. 

Reflection  of  Light. — It  is  well  known  that  when  a  ray  of  light  falls 
upon  a  polished  surface,  such  as  a  mirror,  it  is  reflected  according  to  the 


Air 


Water 

v    /'/•-> 


FIG.  320. 


M 

FIG.    321. 


law  of  reflection,  which  states  that :  the  angle  of  incidence  is  equal  to  the 
angle  of  reflection,  and  the  incidence  and  reflected  rays  lie  in  the  same  plane. 
That  is,  in  Fig.  320,  the  ray  of  light  EX,  from  the  candle  at  E,  impinges 
upon  the  polished  surface  AB  at  X  with  the  angle  of  incidence  EXO  or 
i,  and  is  reflected  to  the  eye  at  D,  the  angle  of  reflection  being  DXO 
or  r.  The  angles  i  and  r  are  equal.  To  the  eye  the  object  appears 
at  E1.  The  line  EE'  is  perpendicular  to  AB  and  the  distances  EP  and 
PE'  are  equal. 

Refraction  of  Light — Single  Refraction. — When  light  passes  obliquely 
from  one  medium  into  another,  for  example,  from  air  into  water,  the 
path  of  the  ray  is  not  straight  but  bent.  That  is,  the  ray  is  refracted. 
We  know  this  from  the  appearance  of  a  rod  or  pencil  placed  in  an  inclined 
position  in  a  glass  or  beaker  of  water.  The  phenomenon  of  refraction  is 
clearly  shown  by  Fig.  321.  The  ray  Dx  in  air  impinges  at  x  upon 

99 


100  MINERALOGY 

the  surface  A  B  and  in  passing  into  the  water  is  bent  or  refracted 
toward  the  normal  OM,  because  the  velocity  of  light  is  less  in  water  than 
in  air.  If  the  angle  of  incidence  DxO  be  represented  by  i  and  the  angle 
of  refraction  MxE  by  r,  then  the  law  of  refraction  may  be  stated  as 
follows  :  the  ratios  between  the  velocities  of  light  V  and  V  in  the  two  media, 
and  the  sines  of  the  angles  of  incidence  and  refraction,  are  equal  and  constant 
for  the  media  concerned,  thus,  in  the  case  of  air  and  water, 

t  ™  f      x-     N          F(air)         sin  i 
n  (Index  of  Refraction)  =  7777^-    £-v  =  '*-,  —  =  1.333. 

V  (water)       gin  r 

The  constant  n  is  called  the  index  of  refraction,  the  velocity  of  light  in  air 
being  taken  as  unity.  Thus,  the  index  of  refraction  of  water  in  terms  of 
air  is  1.3333,  of  the  garnet  1.75,  and  of  the  diamond  2.42.  It  is  evident 
that  the  velocity  of  light  in  a  given  substance  is  proportional  to  the  recip- 
rocal of  its  index  of  refraction.  Hence,  the  larger  the  index,  the  slower 
the  velocity,  and  vice  versa. 

In  determining  these  values  white  light  should  not  be  used,  for  when 
white  light  passes  through  a  prism  it  is  resolved  into  its  component  colors  — 
a  spectrum  is  produced.  Of  these  component  colors,  red  light  is  refracted 
least  and  violet  most.  That  is,  the  velocity  of  light  is  greatest  from  the 
red  end  of  the  spectrum,  and  least  from  the  violet  end.  Indices  of 
refraction  must  therefore  be  determined  for  a  definite  type  of  monochro- 
matic light,  commonly  expressed  in  wave  lengths,  AC//.  Thus,  the  indices 
of  the  diamond  may  be  given  as  follows: 


nred       687,uju  =  2.407 

^yellow    589          =    2.417 
™green      $27          -    2.427 

Wvioiet    397       =  2.465 

The  indices  of  refraction  for  a  certain  variety  glass  are  nred  =  1.524 
and  nvioiet  =  1.545. 

As  sources  of  monochromatic  light,  the  mineralogist  commonly  uses 
non-luminous  gas  flames  colored  by  some  volatile  salt  of  the  following 
elements: 

Lithium,  red  670/x/i 

Sodium,  yellow          589 

Thallium,  green         535 

Dispersion.  —  The  above  examples  are  sufficient  to  show  that  the  in- 
dices of  refraction  for  a  given  substance  vary  considerably  for  the  two 
extremes  of  the  spectrum.  This  difference  in  velocity  is  called  dispersion, 
and  in  the  case  of  the  diamond  it  is  unusually  high  (2.465  —  2.407  =  0.058). 
The  difference  in  the  indices  between  opposite  ends  of  the  spectrum 


CRYSTALLOGRAPHICAL  OPTICAL  J 


101 


indicates  the  strength  of  the  dispersion.     The  dispersion  of  glass  is  much 
lower  (1.545  -  1.524  =  0.021). 

Total  Reflection  and  Critical  Angle.  —  When  light  passes  from  a  denser 
into  a  rarer  medium,  for  example  from  water  into  air,  the  refracted  ray 
is  bent  away  from  the  normal,  Fig.  322.  That  is,  the  angle  of  inci- 
dence I  is  now  smaller  than  the  angle  of  refraction  R.  It  is  therefore 
obvious  that  for  a  definite  angle  of  incidence,  i,  the  angle  of  refraction 
r  may  equal  90°.  This  angle  i  is  called  the  critical  angle,  for  when  the 
angle  of  incidence  exceeds  i  in  value,  as  for  example  7',  the  ray  is  totally 
reflected;  that  is,  it  does  not  enter  the  second  medium,  but  is  reflected 
back  into  the  first,  so  that  angle  /'  equals  angle  R'.  The  value  of  the 
critical  angle  may  be  expressed  as 


sm  i  =  - 
n 


where  n  is  the  usual  index  of  refraction  and  i  the  angle  of  the  incident 
ray  in  the  denser  medium.  Hence,  it  follows  that  substances  with  high 
indices  of  refraction  have  smaller  critical  angles  than  those  with  low 


o  f 


Air 


FIG,  322. 


FIG.  323. 


indices.  The  critical  angle  of  the  diamond  (n  =  2.42)  in  terms  of  air  is 
only  24°26',  while  that  of  water  (n=  1.333)  is  48°36'.  The  phenomenon 
of  total  reflection  is  of  great  importance  in  crystal  optics. 

Double  Refraction.— When  an  oblique  ray  of  light  passes  through 
many  solids  it  is  not  only  refracted  but  also  resolved  into  two  rays,  which 
travel  with  different  velocities.  This  phenomenon  is  designated  as 
double  refraction,  and  is  characteristic  of  all  crystallized  substances  other 
than  those  of  the  cubic  system.  Single  refraction  has  been  discussed 
on  page  99. 

Double  refraction  is  illustrated  in  Fig.  323.  The  ray  DX  is  repre- 
sented as  impinging  upon  a  section  of  the  mineral  calcite,  CaCO3.  DX 
is  resolved  into  two  rays,  o  and  e,  of  which  o  is  the  slower  ray  and  is  re- 
fracted more  than  the  faster  ray  e.  The  velocity  of  the  o  ray  is  the  same 
for  all  directions  in  the  crystal  and  is  called  the  ordinary  ray.  The  other 


102      «    «•  *    ^'^it     t   "-   MINERALOGY 


ray,  e,  is  termed  the  extraordinary  ray.  Its  velocity  varies  with  direc- 
tion. In  the  case  of  calcite,  illustrated  in  figure  323,  the  ordinary  ray 
is  slower  than  the  extraordinary  ray,  but  in  other  substances  the  condi- 
tions may  be  reversed ;  for  example,  zircon. 

Optical  Groups. — Substances  showing  single  refraction  are  called 
singly  refractive  or  isotropic,  while  those  with  double  refraction  are  desig- 
nated as  doubly  refractive  or  anisotropic.  In  isotropic  substances  the 
velocity  of  light  of  a  given  wave  length  does  not  vary  with  direction. 
There  is,  hence,  but  one  index  of  refraction  for  such  substances.  Amor- 
phous substances  and  crystals  of  the  cubic  system  are  isotropic.  Exam- 
ples: diamond  (cubic),  ny  —  2.42;  garnet  (cubic)  ny  =  1.75;  opal 
(amorphous),  nv  =  1.45. 

Anisotropic  substances  are  subdivided  into  two  groups,  depending 
upon  whether  they  possess  one  or  two  isotropic  directions.  These  iso- 
tropic directions  are  called  optic  axes.  Those  with  one  isotropic  direction 
possess  two  principal  indices  of  refraction,  o  and  e,  and  include  crystals 
of  the  hexagonal  and  tetragonal  systems.  Examples :  calcite  (hexagonal) , 
o  =  1.65,  e  =  1.48;  zircon  (tetragonal)  o  =  1.924,  e  =  1.968.  These 
substances  have  one  optic  axis  and  are  also  called  uniaxial.  The  direc- 
tion of  the  optic  axis  is  that  of  c  crystallographic  axis.  If  the  index  o  is 
greater  than  e,  the  crystal  is  said  to  be  optically  negative,  and  optically 
positive  when  e  has  the  larger  value.  Compare  the  values  above  for 
calcite  and  zircon.  The  difference  between  the  indices  of  the  ordinary 
and  extraordinary  rays  gives  the  strength  of  double  refraction  or  birefrin- 
gence. Thus  for  calcite  it  is  (0)  1.65  —  (e)  1.48  =  0.17;  for  quartz  it  is 
(e)  1.553  —  (o)  1.544  =  0.009.  The  birefringence  is  characterized  as 
strong  or  weak,  depending  upon  the  values  obtained. 

Those  anisotropic  crystals  which  possess  two  isotropic  directions,  or 
optic  axes,  are  called  biaxial.  They  include  all  crystals  belonging  to 
the  orthorhombic,  monoclinic,  and  triclinic  systems.  In  these  crystals 
there  are  three  principal  optical  directions  at  right  angles  to  each  other, 
parallel  to  which  light  is  propagated  with  velocities  indicated  by  the 
three  indices,  a,  ft,  7.  Examples:  topaz  (orthorhombic),  a  =  1.607, 
ft  =  1.610,  7  =  1.618;  epidote  (monoclinic),  a  =  1.730,  ft  =  1.754 
7  =  1.768;  axinite  (triclinic)  a  =  1.672,  ft  =  1.678,  7  =  1.681.  When 
ft  approaches  in  value  a  more  than  it  does  7,  as  in  the  case  of  topaz,  the 
substance  is  optically  positive.  In  optically  negative  crystals  the  value 
of  ft  lies  nearer  to  7,  as  is  shown  by  the  indices  of  epidote  and  axinite. 
The  double  refraction  or  birefringence  of  biaxial  crystals  is  indicated  by 
7-«;  thus,  for  topaz  it  is  1.618  -  1.1607  =  0.011. 

These  optical  properties  may  be  summarized  as  follows: 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS 


103 


Singly  refractive 
or  Isotropic 


|  Amorphous  Substances  and 
I  Cubic  Crystals 


Doubly  refractive  or  Aniso- 
tropic 


Hexagonal 
Tetragonal 


Orthorhombic 
Monoclinic 
Triclinic  crystals 


Uniaxial 


Biaxial 


One  index  of  refrac- 
tion, 71. 

Two    indices    of    re- 
fraction, o  and  e. 

Positive  o<e 
Negative  e<o 

*Three  indices  of  re- 
fraction, a,  /3,  7. 

Positive,  a£,    7 
Negative  «,   /3y 


FIG.  324. 


FIG.  325. 


Polarizing  Microscope. — As  indicated  on  page  99,  the  microscope  used 
by  mineralogists  (Fig.  324)  differs  materially  from  the  instruments 
used  by  biologists  and  other  scientists,  in  that  the  stage  rotates  in  the  hori- 
zontal plane.  It  is  also  equipped  with  devices,  called  Nicol  prisms,  which 
permit  objects  to  be  studied  in  polarized  light.  Figure  325  shows  a 


104 


MINERALOGY 


polarizing  microscope  in  cross-section.  T  is  the  rotating  stage.  Below 
the  stage  is  P,  a  Nicol  prism  for  the  production  of  polarized  light,  see 
page  99.  It  is  called  the  polarizer.  Another  Nicol  prism,  Q,  is  placed 
above  the  stage  in  the  tube  of  the  microscope.  This  is  called  the  analyzer. 
This  second  Nicol  prism  is  mounted  upon  a  slide  so  that  it  may  be  easily 
removed  from  the  tube.  Both  nicols  can  usually  be  rotated. 

There  are  several  classes  of  observations  which  can  be  made  with  a 
mineralogical  microscope,  viz. : 

I.  General  observations  in  ordinary  light. 

II.  Observations  in  polarized  light. 

(a).  Parallel  polarized  light. 
(6).  Convergent  polarized  light. 

I.  GENERAL  OBSERVATIONS  IN  ORDINARY  LIGHT 

Centering. — In  order  to  use  the  rotating  stage  to  advantage,  its 
center  must  obviously  lie  in  the  vertical  axis  passing  through  the  tube 

when  the  stage  is  rotated.  To  permit  of 
centering,  the  tube  is  provided  with  two 
screws  placed  at  right  angles  to  each  other 
directly  above  the  objective.  These  screws 
displace  the  tube  laterally. 

Centering  is  most  readily  accomplished 
by  placing  on  the  stage  an  object  glass 
with  a  dark  speck  or  small  spot  of  ink,  and 
noting  the  position  of  the  speck  with  respect 
to  the  dark  lines  crossing  the  field.  These 
are  called  cross  hairs  and  their  intersection 
indicates  the  center  of  the  field  of  vision. 
The  object  glass  should  then  be  carefully 
moved  until  the  speck  is  at  the  intersection 
of  the  cross  hairs.  If  the  stage  is  centered, 
Wright  (1877—).  Geophysical  the  k  will  remain  at  the  intersection 

Laboratory,    Washington,    D.C.  v .  .  . 

American  authority  on  the  polar-     when    the    stage    IS    rotated.      If    it     IS     not 

izing  microscope  and  its  appiica-    centered,  the  speck  will  move  in  a  circular 

tions.  . 

path,   the   center  of  which,   o,  lies  to  one 

side  of  the  center  of  the  field  of  vision,  7  (Fig.  327).  The  stage  should 
then  be  rotated  until  the  speck  appears  to  lie  upon  one  of  the  cross  hairs, 
A',  and  the  screw  parallel  to  it,  C,  should  then  be  turned  until  the 
speck  has  moved  from  X  to  F,  that  is,  one-half  the  distance  to  the 
intersection  of  the  cross  hairs.  The  object  glass  is  now  moved  so  that 
the  speck  is  again  at  the  center  of  the  field,  and  the  stage  rotated.  The 
speck  will  describe  the  path  indicated  by  the  smaller  circle.  When  it 
apparently  lies  on  the  second  cross  hair,  P',  the  screw,  D,  should  be  turned 


FIG.  326.— Frederick    E. 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS 


105 


until  it  has  moved  from  Xf  to  F',  again  one-half  the  distance  to  the  center 
of  the  field.  Upon  bringing  the  speck  to  the  center  of  the  field  and  rotat- 
ing the  stage,  it  will  be  found  that  it  has  been  centered ;  that  is,  the  spot 
will  remain  stationary.  Ordinarily,  it  is  necessary  to  repeat  this  process 
several  times  before  the  stage  is  perfectly  centered. 

On  some  microscopes  the  centering  screws  are  not  parallel  to  the  cross 
hairs,  as  in  Fig.  327,  but  are  placed  diagonally,  as  shown  in  Fig.  328. 


When  this  is  the  case  the  speck  should  be  brought  into  the  diag- 
onal positions  indicated  by  X  and  X',  and  the  adjustments  made  by  the 
screws  C  and  D,  as  described  above. 

Measurement  of  Angles. — In  measuring  plane  angles  between  crystal 
edges  or  between  cleavage  directions,  the  intersection  of  the  edges  is 
brought  to  the  center  of  the  cross  hairs  and  the  microscope  centered,  as 
described  above.  The  stage  is  now  rotated  until  one  edge  is  parallel  to 
one  cross  hair,  A,  and  a  reading  made  on  the  gradu- 
ated scale  of  the  stage.  See  Fig.  329.  The  stage  is 
then  rotated  until  the  other  edge  is  parallel  with  the 
same  cross  hair,  A  A' .  The  difference  between  the 
two  readings,  angle  m,  is  the  supplement  of  the  plane 
angle  under  consideration  drawn  in  heavy  lines. 

Becke  Method. — The  indices  of  refraction  of 
solids,  either  in  the  form  of  rock  or  mineral  sections 
or  fragments,  may  be  easily  determined  by  using  the 
method  devised  by  Becke  (Fig.  330).  This  method  depends  upon  total 
reflection  of  light,  as  illustrated  in  Fig.  331.  Let  A  and  B  be  two 
solids  in  contact,  B  having  a  higher  index  of  refraction  than  A.  «  If 
the  microscope  be  focused  upon  the  contact,  a  band  or  line  of  light 
will  be  observed  at  SO,  which  will  move  toward  B  when  the  tube 
is  raised.  On  lowering  the  tube  it  moves  toward  A.  This  band 
or  zone  is  caused  by  the  concentration  of  light  on  one  side  of  the 
contact,  for  all  rays  of  light  in  A,  which  impinge  upon  the  contact, 


106 


MINERALOGY 


will  pass  into  B,  irrespective  of  the  angle  of  incidence,  i.  Thus,  the  ray 
x  will  emerge  as  OM.  But  when  light  passing  through  B  impinges 
upon  the  contact,  the  size  of  the  angle  of  incidence  is  of  great  importance, 
for  here  the  passage  is  from  a  denser  to  a  rarer  medium.  In  all  such 
cases  total  reflection  will  take  place  if  the  angle  of  incidence  i  is  larger 
__  __  than  the  critical  angle.  That  is,  the  ray 
R  will  emerge  as  ST.  As  indicated,  the 
raising  of  the  microscope  tube  will  displace 
the  band  of  light,  due  to  this  concentration 
of  rays,  toward  the  substance  with  the 
higher  index.  The  intensity  of  this  line  of 
light  is  often  accentuated  by  lowering  the 
substage  of  the  instrument.  Whether  or 
not  the  index  of  the  substance  under  in- 
vestigation is  higher  or  lower  than  that  of 
a  known  substance  can  thus  be  easily  deter- 
mined. 

The  indices  of  refraction  of  fragments 
can  be  determined  by  embedding  them  in 
liquids  of  known  indices,  and  the  movement 
of  the  band  of  light  noted.  The  operation 
is  repeated  with  different  liquids,  until  one 

is   found  with  an  index  e(ual  to  that  °f  the 


mineralogy  and  petrography  in    fragment.     In  this  case  the  fragment  is  in- 

visible, or  only  slightly  visible,  and  is  said 

to  have  low  relief.  When  the  difference  between  the  indices  of  the  frag- 
ment and  the  liquid  is  quite  large,  the  fragment  appears  rough  with  a 
dark  border,  and  is  said  to  have  high  relief.  For  this  purpose  the 
following  liquids  are  serviceable: 


A              _£J 

Lower         .       I 

fco_                 B 

\       fT     Higher 

FIG.  331. 

Water 1 . 3336 

Petroleum 1 . 45 

Turpentine 1 . 4721 

Xylol,  meta 1 . 502 

Clove  oil ' 1 . 544 

Cinnamon  oil 1 . 6026 

a.  monobromnaphthalene 1 . 6495 

Methyelene  iodide 1 . 7421 

Sulphur  in  methylene  iodide 1.8 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS  .   107 

A  set  of  standardized  liquids  with  indices  which  vary  regularly  is 
practically  indespensible  in  determining  the  indices  of  refraction  of  small 
fragments.  Wright  suggests  the  use  of  the  following: 

Mixture  of  Index 

Petroleum  and  turpentine 1 . 450-1 . 475 

Turpentine  and  clove  oil 1 . 480-1 . 535 

Clove  oil  and  a.  monobromnaphthalene 1 . 540-1 . 635 

a  monobromnaphthalene  and  a  monochlornaphthalene 1 . 640-1 . 655 

Monochlornaphthalene  and  methylene  iodide 1 . 660-1 . 740 

Sulphur  dissolved  in  methylene  iodide 1 . 740-1 . 790 

Methylene  iodide,  antimony  iodide,  arsenic  sulphide,  antimony  sul- 
phide, and  sulphur 1 . 790-1 . 960 

II.  OBSERVATIONS  IN  POLARIZED  LIGHT 

Nature  of  Polarized  Light. — According  to  the  undulatory  theory,  light 
is  assumed  to  be  a  form  of  energy  transmitted  in  waves  in  the  ether,  which 
pervades  all  things  and  space.  The  propagation 
of  light  takes  place  according  to  the  laws  of  wave 
motion,  the  ether  particles  vibrating  at  right 
angles  to  the  direction  of  propagation.  The  ve- 
locity of  propagation  has  been  determined  to  be 
about  186,000  miles  per  second. 

In  the  case  of  ordinary  light,  the  vibration  of 
the  ether  particles  takes  place  in  a  plane  at  right 
angles  to  the  direction  in  which  the  light  is  pro- 
pagated, but  the  vibration  direction  in  this  plane 

is  constantly  changing.  If  in  Fig.  332,  a  ray  of  light  is  considered  as 
being  propagated  perpendicular  to  the  plane  of  this  page,  then  the  vi- 
bration of  the  ether  particles  will  be  successively  in  the  directions  A  A', 
BB',  CC',  and  so  forth.  This  is  shown  in  perspective  in  Fig.  333,  which 
must  be  conceived  as  revolving  about  AB  as  an  axis. 

In  plane  polarized  light,  the  vibrations  take  place  in  a  definite  direc- 
tion within  the  plane  and  at  right  angles  to  the  direction  of  propagation. 
Plane  polarized  light  may  be  produced  in  three  ways:  (1)  by  absorption, 
(2)  by  reflection,  and  (3)  by  refraction. 

Polarized  Light  by  Absorption. — When  ordinary  light  passes  through 
a  plate  of  colored  tourmaline  cut  parallel  to  the  c  axis,  the  light  which 
emerges  is  plane  polarized.  Its  vibrations  are  commonly  assumed  to  be 
parallel  to  the  c  axis.  This  is  illustrated  in  Fig.  334.  Ordinary  light 
emanating  from  A  vibrates  in  all  directions,  but  in  order  to  pass  through 
the  tourmaline  plate  xy,  it  must  only  vibrate  parallel  to  the  c  axis, 
that  is,  parallel  to  xy.  Light  vibrating  in  other  directions  is  absorbed 
by  the  tourmaline.  Hence,  op  represents  a  ray  of  plane  polarized  light 
produced  by  absorption. 


108 


MINERALOGY 


If  a  second  plate  of  tourmaline  x'y'  be  placed  in  the  path  of  op  so 
that  the  direction  of  its  c  axis  is  perpendicular  to  that  of  the  first  plate  xy, 
we  shall  observe  that  the  ray  op  vibrating  vertically  will  now  be  entirely 
absorbed  by  the  second  tourmaline,  the  favorable  direction  for  the  pas- 


FIG.  333. 


sage  of  light,  x'y' ,  being  horizontal.     This  method  for  the  production  of 
polarized  light  is  not  commonly  used  in  scientific  instruments. 

Polarized  Light  by  Reflection. — When  ordinary  light  is  reflected  from 
a  smooth  surface,  such  as  glass,  it  is  found  to  be  partially  plane  polarized, 


the  vibration  directions  being  at  right  angles  to  the  direction  of  propaga- 
tion. In  Fig.  335,  the  plane  ABCD,  containing  the  incident  and  reflected 
rays  ax  and  xy,  is  called  the  plane  of  polarization.  The  plane,  MPON, 
in  which  the  polarized  ray  xy  vibrates,  is  called  the  plane  of  vibration. 


FIG.  335. 


FIG.  336. 


It  is  perpendicular  to  the  plane  of  polarization.  This  method  of  produc- 
ing polarized  light  was  formerly  used  much  more  extensively  than  at 
present. 

Polarized  Light  by  Refraction. — A  portion  of  the  ray  AX  in  Fig. 
336,  may  enter  the  plate  at  X  and  be  refracted.  Upon  emerging  as 
the  ray  LC,  it  is  partially  plane  polarized.  The  vibrations  are  now  exe- 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS 


100 


A 


cuted'  in  the  plane  of  polarization,  and  are  perpendicular  to  the  vibration 
directions  characteristic  of  polarization  by  reflection.  The  polarized 
light  used  in  the  mineralogical  microscope  is  commonly  produced  by 
refraction.  For  this  purpose,  a  nicol  prism  is  usually  employed. 

Nicol  Prism. — This  consists  of  a  cleavage  piece  of  clear,  transparent 
calcite,  commonly  called  Iceland  or  double  spar.  It  is  usually  somewhat 
elongated  as  shown  in  Fig.  337.  The  natural  angles  of  71°  at  A  and 
F  are  reduced  by  grinding  to  68°.  The  prism  is  then  cut  in  two  by  the 
plane  CD,  which  is  at  right  angles  to  the  new  end  faces  BC  and  DE. 
After  the  two  parts  have  been  polished,  they  are  cemented 
together  with  Canada  Balsam  DC,  which  has  an  index  of 
refraction  of  about  1.54. 

If  ordinary  light  be  allowed  to  fall  upon  DE  in  the  di- 
rection of  M N,  it  will  be  resolved  into  two  rays,  since  cal- 
cite is  a  doubly  refractive  substance.  Each  of  these  rays 
is  plane  polarized.  One  of  the  rays  is  called  the  ordinary 
ray,  o.  It  has  a  constant  index  of  refraction  of  1.658. 
The  other  ray  is  termed  the  extraordinary  ray  e  and  its 
index  of  refraction  varies  from  1.486,  when  propagated  at 
right  angles  to  the  c  axis,  to  1.658  when  parallel  to  the  c 
axis.  In  the  direction  NR,  its  index  of  refraction  approxi- 
mates that  of  the  Canada  balsam. 

The  ordinary  ray  o  with  an  index  of  refraction  1.658 
impinges  upon  the  film  of  Canada  balsam  at  S  with  an  angle 
of  incidence  which  is  greater  than  the  critical  angle.  It  is, 
hence,  totally  reflected  in  the  direction  of  ST.  It,  therefore, 
does  not  emerge  at  the  upper  end  of  the  nicol  prism,  but 
is  absorbed  by  the  side  of  the  case  in  which  the  nicol  is 
mounted. 

The  extraordinary  ray  e,  however,  pursues  a  path  in  the  nicol  indi- 
cated by  NR.  For  this  direction  the  index  of  refraction  of  the  extra- 
ordinary ray  is  approximately  the  same  as  that  of  the  Canada  balsam 
and  the  ray,  therefore,  passes  through  the  balsam  with  little,  if  any, 
deviation.  It  emerges  from  the  prism  at  W,  and  is  plane  polarized  with 
vibrations  parallel  to  the  short  diagonal  of  the  end  rhombohedral  face  of 
the  nicol.  This  simple  device  is  very  efficient  for  producing  plane 
polarized  light  by  refraction. 

Nicol  prisms  are  used  very  extensively  in  polarizing  microscopes 
and  other  crystallographic-optical  instruments.  In  microscopes,  a 
nicol  prism,  called  the  polarizer,  is  placed  below  the  stage,  while  a  second, 
the  analyzer,  is  mounted  in  the  tube  above  the  objective  (see  page  103). 
The  nicols  can  be  rotated  in  the  horizontal  plane.  Observations  may  be 
made  with  the  vibration  directions  of  both  nicols  either  parallel  or  at 
right  angles  to  each  other.  When  the  directions  are  perpendicular  to 


FIG.  337. 


110  MINERALOGY 

each  other,  the  nicols  are  said  to  be  crossed.  Observations  with  crossed 
nicols  are  much  more  important  than  those  made  with  parallel  nicols. 
Parallel  and  Convergent  Polarized  Light. — Observations  may  be 
carried  out  with  the  rays  of  polarized  light  passing  through  the  sub- 
stances parallel  to  the  axis  of  the  microscope  tube,  or  the  rays  may  be 
made  to  converge  in  the  substance  by  means  of  suitable  condensing  lenses. 
We  may  hence  speak  of  observations  in  (a)  parallel  polarized  light,  and 
in  (b)  convergent  polarized  light. 

Since  solids  may  be  classified  optically  as  isotropic  and  anisotropic, 
the  effects  of  parallel  and  convergent  polarized  light  upon  each  of  these 
groups  will  be  considered.  It  must  be  remembered  that  anisotropic 
substances  can  be  subdivided  into  uniaxial  and  biaxial  groups. 

Behavior  of  Isotropic  Substances,  (a)  In  Parallel  Polarized  Light 
with  Crossed  Nicols. — If  the  analyzer  is  removed  from  the  microscope 
tube  and  an  isotropic  substance,  either  an  amorphous  substance  or  a 
crystal  of  the  cubic  system,  be  viewed  on  the  microscope  stage,  it  will 
be  noted  that  the  field  of  vision  is  illuminated.  It  remains  illuminated 
for  all  positions  of  the  stage,  for  the  polarized  light  emerging  from  the 
polarizer  passes  through  an  isotropic  substance  without  change.  How- 
ever, when  the  analyzer  is  replaced  with  its  vibration  direction  per- 
pendicular to  that  of  the  polarizer,  the  field  of  vision  is  dark  and  remains 
so  upon  rotating  the  stage.  This  is  due  to  the 
fact  that  the  light  emerging  from  the  object  on 
the  stage  vibrates  parallel  to  the  vibration  direc- 


FIG.  338.  tion  of  the  polarizer.  This  direction,  however, 

is  at  right  angles  to  that  of  the  analyzer,  the 

nicols  being  crossed,  and  hence  no  light  passes  through  the  upper  nicol. 
All  isotropic  substances,  therefore,  appear  dark  between  crossed  nicols. 
This  observation  is  very  easily  made  and  serves  to  distinguish  isotropic 
substances  from  those  which  are  optically  anisotropic  or  doubly  re- 
fractive. 

(b)  In  Convergent  Polarized  Light  with  Crossed  Nicols. — When  sub- 
stances are  studied  in  convergent  polarized  light,  the  rays  of  light  pass 
through  the  substance  inclined  to  the  axis  of  the  microscope;  that  is, 
they  tend  to  converge  (Fig.  338).  Convergent  light  is  easily  obtained 
by  using  an  objective  of  high  magnification  and  inserting  a  condensing 
lens  below  the  microscope  stage.  . 

Isotropic  substances  appear  dark  in  convergent  light  between  crossed 
nicols  for  the  same  reasons  as  given  above.  That  is,  between  crossed 
nicols  they  are  always  dark  in  both  parallel  and  convergent  light. 

Behavior  of  Uniaxial  Substances  in  Parallel  Polarized  Light  with 
Crossed  Nicols.  (a)  Sections  perpendicular  to  the  c  Axis. — When  the 
analyzer  is  removed,  these  sections  of  uniaxial  crystals,  that  is,  either 
crystals  of  the  hexagonal  or  tetragonal  systems,  will  appear  light  and 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS 


111 


remain  so  for  all  positions  of  the  stage.  When  the  analyzer  is  replaced 
with  its  vibration  directions  perpendicular  to  that  of  the  polarizer,  the 
field  is  dark  and  remains  so  when  the  stage  is  rotated.  This  behavior  of 
hexagonal  and  tetragonal  crystals  is  the  same  as  for  isotropic  substances, 
as  discussed  above.  This  is  due  to  the  fact  that  the  light  passing  through 
the  crystal,  or  through  the  section,  is  parallel  to  the  c  axis  which  is  an 
isotropic  direction.  For  this  particular  direction,  uniaxial  substances 
behave  in  parallel  polarized  light  as  though  they  were  isotropic. 

(b)  Sections  Parallel  or  Inclined  to  the  c 
Axis. — When  these  sections  are  viewed  with 
the  analyzer  removed,  the  field  of  vision  is 
illuminated.  When  the  analyzer  is  replaced 
and  the  stage  rotated,  the  field  is  four  times  , 
light  and  four  times  dark  during  a  complete  |j — 
rotation,  provided  the  nicols  are  crossed. 
That  is,  when  viewed  in  daylight  or  white 
artificial  light,  interference  colors  are  seen 
four  times  during  a  complete  rotation.  The 
positions  of  greatest  darkness  or  extinction 
indicate  the  vibration  directions  of  the  rays 
passing  through  the  section  or  crystal.  When  the  vibration  directions 
of  the  crystal  and  those  of  the  nicols  are  parallel,  the  field  of  vision  is 
dark.  This  is  illustrated  in  Fig.  339  where  PP'  and  AA'  are  the 
vibration  directions  of  the  polarizer  and  analyzer  respectively,  and  RR' 
and  SS'  those  of  the  crystal.  PP'  and  RR'  being  parallel,  light  from 
the  polarizer  passes  through  the  crystal  without  change  in  vibration 
direction  and  enters  the  analyzer  but  does  not  emerge,  the  favorable 
direction  for  passage  through  the  upper  nicol  being  A  A'. 


FIG.   339. 


FIG.  340. 


FIG.  341. 


The  cross  hairs  of  the  microscope  are  parallel  to  the  vibration  direc- 
tions of  the  nicols  and  are  used  for  the  determination  of  the  extinction  or 
vibration  directions  in  the  crystal  or  section.  Extinction  may  take  place 
when  the  cross  hairs  are  parallel  or  perpendicular  to  the  edges  of  the 
specimen  as  in  Fig.  340.  When  this  is  the  case,  the  crystal  is  said 
to  have  parallel  extinction.  Uniaxial  substances  may  also  possess  sym- 
metrical extinction  as  illustrated  in  Fig.  341. 

(c)  Determination  of  Indices  of  Refraction. — The  position  of  extinction 
is  found  as  indicated  above.  The  analyzer  is  then  removed  and  the  Becke 


112 


MINERALOGY 


test  applied  (see  page  105).  In  this  way,  the  index  of  refraction  of 
the  ray  vibrating  parallel  to  the  vibration  direction  of  the  polarizer  is 
determined.  On  rotating  the  stage  through  90°,  the  index  of  refraction 
for  the  second  vibration  direction  can  be  determined.  The  ray  vibrating 
parallel  to  the  c  axis  is  termed  the  extraordinary  ray  e;  the  one  vibrating 
at  right  angles  to  it,  the  ordinary  ray  o.  When  the  index  of  refraction  of  e 
is  larger  than  that  of  o,  the  crystal  is  said  to  be  optically  positive;  when 
smaller,  optically  negative  (see  page  102). 

(d)  Interference  Colors. — When  the  vibration  directions  in  the  crystal 
are  not  parallel  to  those  of  the  nicols,  the  field  shows  in  general  an  inter- 
ference color,  provided  the  crystal  is  viewed  in  either  daylight  or  arti- 
ficial white  light.  The  color  is  due  to  the  fact  that  the  light  from  the 
polarizer  PP'  is  resolved  into  two  rays  vibrating  parallel  to  xxr  and  yyf, 
the  vibrations  direction  of  the  crystal  (Figs.  342  and  343).  The 
two  rays  in  the  crystal  travel  with  different  velocities  and  when  they 
emerge  the  slow  ray  naturally  lags  behind  the  faster.  On  entering  the 


y^ — 


FIG.  342. 

upper  nicol,  each  of  these  rays  is  further  resolved  into  two  rays  vibrat- 
ing parallel  to  the  vibration  directions  of  the  o  and  e  rays  of  the  analyzer. 
As  indicated  on  page  109,  only  the  latter  of  these,  namely  the  two  vibrating 
parallel  to  the  e  ray,  emerge  from  the  analyzer.  But  these  two  emergent 
rays  (OS  and  OR)  vibrating  in  the  same  plane,  travel  with  different 
velocities.  Interference  of  light  is  thus  brought  about,  and  with  crossed 
nicols  when  the  phasal  difference  of  the  two  rays  is  equal  to  a  whole  wave 
length  7,  or  some  whole  multiple  thereof,  destructive  interference  results 
(Fig.  342).  When  the  phasal  difference  is  a  half  wave  length,  ^7, 
or  some  odd  multiple  thereof,  the  rays  reinforce  each  other  (Fig.  343). 
As  the  phasal  differences  for  the  component  colors  of  white  light 
will  be  of  both  these  types,  certain  portions  of  the  white  light  passing 
through  the  crystal  are  destroyed,  while  other  portions  are  intensified 
causing  the  light  which  emerges  to  be  colored.  The  field  of  vision  shows 
therefore  what  is  commonly  designated  as  an  interference  color.  The 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS  113 

character  of  the  color  depends  upon  (1)  strength  of  double  refraction  of 
the  substance,  (2)  position  of  the  plate  with  regard  to  the  c  axis  and  (3) 
thickness* of  the  plate.  When  monochromatic  light  instead  of  daylight 
is  used,  the  field  will  be  dark  as  before,  if  the  vibration  directions  in  the 
substance  and  nicols  correspond.  In  intermediate  positions,  the  field 
will  be  illuminated  by  light  of  the  particular  color  employed. 

(e)  Determination  of  the  Fast  and  Slow  Rays. — The  position  of  extinc- 
tion is  first  determined  and  the  stage  then  rotated  so  that  the  extinction 
directions  cross  the  field  diagonally;  that  is,  they  make  angles  of  45°  with 
the  cross  hairs  (Fig.  344).  This  is  the  position  of  most  intense  illumina- 
tion and  color.  Into  the  slot  of  the  microscope  tube,  which  is  directly 
above  the  object,  a  gypsum  or  selenite  test  plate  is  now  inserted.  When 
viewed  alone  between  cross  nicols,  the  test  plate  yields  an  interference 
color  which  is  usually  designated  as  the  sensitive  red  tint.  This  tint  is 
easily  changed  to  either  blue  or  yellow  by  the  action  of  the  crystal  on  the 
stage.  If  it  is  changed  to  blue,  it  means 
that  the  vibration  directions  of  the  test 
plate  and  those  of  the  crystal  correspond; 
that  is,  the  slow  ray  in  the  test  plate  is  over 
the  slow  ray  in  the  crystal,  and  fast  over 
fast.  Now  note  the  direction  of  the  marked  A 
ray  on  the  test  plate  which  is  usually  given 
as  a  or  a.  This  is  the  fast  ray  and  the  vibra- 
tion direction  at  right  angles  to  it  is  obviously 
that  of  the  slow  ray,  which  is  commonly 
designated  as  c  or  a  In  this  way,  the  direc- 

•  'i  I1  IG.   o44. 

tion    of    the    corresponding  rays   are  easily 

recognized  in  the  crystal.  If,  however,  the  sensitive  red  tint  is  changed 
to  yellow,  instead  of  blue,  it  means  that  the  fast  ray  of  the  test  plate 
is  over  the  slow  ray  of  the  crystal,  and,  vice  versa. 

(/)  Order  of  Interference  Colors. — The  interference  colors  may  be 
bright  and  vivid  and  are  then  said  to  be  of  a  low  or  medium  order,  or  they 
may  be  hazy  and  dull  and  are  of  the  higher  orders.  It  is  well  in  deter- 
mining the  order  of  interference  colors  to  study  an  interference  color  chart. 
When  the  color  approximates  white,  it  is  characterized  as  being  white  of 
the  higher  order.  When  sections  of  different  substances  have  the  same 
thickness,  some  indication  of  the  strength  of  double  refraction,  or  bi- 
refringence, can  be  obtained  from  the  character  of  the  interference  colors, 
for  the  stronger  the  double  refraction,  the  higher  the  resultant  colors. 
When  dealing  with  one  and  the  same  substance,  the  thicker  sections  or 
crystals  will  show  colors  of  the  higher  orders. 

The  Behavior  of  Uniaxial  Crystals  in  Convergent  Polarized  Light 
with  Crossed  Nicols.  (a)  Sections  Perpendicular  to  the  cAxis. — In  uniaxial 
substances  all  rays  of  light  inclined  to  the  c  axis  are  resolved  into  two 

8 


114 


MINERALOGY 


rays,  o  and  e,  which  travel  with  unequal  velocities.  These  rays  interfere 
therefore  on  emerging  from  the  substance,  as  indicated  in  Fig.  345. 
The  phasal  difference  between  these  rays  increases  with  the  inclination  of 
the  incident  rays  to  the  c  axis.  Hence,  at  OP,  which  corresponds  to  the 
direction  of  the  c  axis,  the  phasal  difference  will  be  zero.  Accordingly, 
the  phasal  difference  increases  as  the  distance  of  emergence  from  P  grows 
larger.  The  increase  is  the  same  for  all  directions.  Wherever  the  phasal 

difference  A  =  ^X,  where  n  is  odd,  reinforcement  of  light  takes  place. 

z 

Where  A  =  n\,  n  being  any  whole  number,  destructive  interference  re- 
sults. Therefore,  along  any  diameter  through  the  field  of  vision,  we  will 


observe  darkness  at  the  center  P,  and  at  equal  distances  on  either  side  of 
P  the  same  interference  colors  will  appear  when  daylight  or  artificial 
white  light  is  used.  In  uniaxial  crystals,  all  directions  perpendicular  to 
the  c  axis  are  optically  the  same.  Hence,  the  interference  colors  appear 
as  a  series  of  concentric  rings.  The  colors  are  brighter  and  more  vivid 
near  the  center  of  the  field  and  gradually  fade  as  the  distance  from  the 
center  increases.  These  isochromatic  circles  are  farther  apart  near  the 
center  of  the  field  and  closer  together  toward  the  periphery.  In  mono- 
chromatic light,  a  series  of  light  and  dark  circles  will  be  observed  (Figs. 
346  and  347). 

It  will  be  further  observed  that  a  dark  cross  lies  superimposed  upon 
the  isochromatic  circles.  The  cross  occurs  where  the  vibration  directions 
of  the  substance  correspond  to  those  of  the  nicols,  for  as  has  been  pointed 
out  previously,  in  such  instances  the  field  is  dark.  The  isochromatic 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS 


115 


circles  and  the  dark  cross  constitute  what  is  called  a  uniaxial  interference 
figure. 

The  uniaxial  interference  figure  remains  unchanged  when  the  stage 
is  rotated,  for  all  directions  through  the  substance  perpendicular  to  the  c 
axis  are  alike  optically.  In  order  to  observe  interference  figures,  it  is 


FIG.  346. 


FIG.  347. 


necessary  to  either  remove  the  eyepiece  of  the  microscope,  or  to  insert  an 
auxiliary  lens  called  the  Bertrand  lens  into  the  tube  above  the  analyzer. 
In  the  first  case,  the  figure  is  small  and  appears  far  down  in  the  tube.  It 
is,  however,  usually  quite  distinct.  In  the  second  case,  the  figure  is 
much  larger,  but  generally  more  hazy. 


FIG.  348. 

(b)  Sections  Inclined  to  the  c  Axis. — Sections  of  this  character  show  only 
a  partial  interference  figure  in  convergent  light.  The  more  nearly  the 
section  is  parallel  to  the  base,  the  more  will  the  observed  figure  approxi- 
mate the  normal  figure;  and  the  greater  the  departure  from  this  parallel- 
ism, the  more  the  figure  will  be  eccentric  and  incomplete.  This  is  shown 


116 


MINERALOGY 


by  Fig.  348.  When  the  stage  is  rotated,  the  arms  of  the  dark  cross 
move  across  the  field  parallel  to  the  cross  hairs  and  in  the  same  direction 
as  the  movement  of  the  stage.  This  observation  is  of  great  importance 
in  distinguishing  certain  uniaxial  from  biaxial  figures  (see  page  1 19) . 

(c)  Strength  of  Double  Refraction  Determined  from  Uniaxial  Interference 
Figures. — The  number  of  isochromatic  circles  may  serve  to  estimate  the 
strength  of  double  refraction  or  birefringence.     When  sections  have  the 
same  thickness,   substances   with   strong  double  refraction  will  show 
more  rings  than  those  possessing  weak  birefringence.     Thickness  also  in- 
creases the  number  of  rings  (Figs.  346  and  347).     In  extremely  thin 
sections  no  rings  at  all  are  sometimes  visible.     This  is  especially  true 
of  substances  with  very  weak  birefringence. 

(d)  Character  of  Double  Refraction  Determined  from  Uniaxial  Interference 
Figures. — If  the  mica  test  plate  be  inserted  in  the  slot  of  the  microscope 
tube,  it  will  be  observed  that  the  interference  figure  breaks  up  and  two 
distinctly  black  spots  appear  near  the  center  of  the  field.     The  position 
of  these  spots  with  respect  to  the  vibration  direction  marked  on  the  test 


Blue 


Yellow 


Yellow 


FIG.  349. 


FIG.  350. 


FIG.  351. 


plate  should  be  noted.  If  a  line  joining  these  spots  is  parallel  to  the  c 
direction  (slow  ray  in  test  plate),  the  substance  is  optically  negative  (Fig. 
349) .  When  the  gypsum  or  selenite  test  plate  is  used,  two  blue  spots  ap- 
pear. If  the  line  joining  these  blue  spots  is  parallel  to  the  a  direction  of  the 
gypsum  test  plate  (fast  ray  in  test  plate) ,  the  substance  is  said  to  be  optic- 
ally negative  (Fig.  350).  In  case  of  optically  positive  substances,  the 
line  joining  the  black  and  blue  spots  crosses  the  marked  direction  on 
the  plates  referred  to  above,  (Fig.  351).  These  observations  are  based 
upon  the  fact  that  when  like  directions  in  the  test  plates  and  substances 
are  over  one  another,  the  double  refraction  is  increased.  When  the 
corresponding  directions  are  unlike,  for  example,  fast  ray  over  slow  ray, 
and  vice  versa,  a  reduction  in  double  refraction  results. 

General  Statement  Regarding  Biaxial  Crystals. — As  indicated  on 
page  102,  all  crystals  of  the  orthorhombic,  monoclinic,  and  triclinic 
systems  are  biaxial  and  possess  three  principal  optical  directions  at 
right  angles  to  each  other.  In  the  orthorhombic  system  these  optical 
directions  correspond  to  the  three  crystallographic  axes.  Monoclinic 
crystals  have  only  one  of  these  directions  fixed,  namely,  by  the  b  crystal- 
lographic axis.  In  the  triclinic  system,  there  is  no  relationship  between 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS  117 

the  orientation  of  the  principal  optical  directions  and  the  crystallographic 
axes.  The  principal  optical  direction  which  bisects  the  acute  angle 
between  the  two  isotropic  directions,  or  the  optic  axes,  is  called  the  acute 
bisectrix,  Bxa.  The  obtuse  bisectrix  Bx0,  bisects  the  obtuse  angle  of  the 
optic  axes.  These  bisectrices  are  the  vibration  directions  of  the  rays 
traveling  with  the  greatest  and  least  velocities.  The  direction  at  right 
angles  to  the  plane  of  these  bisectrices  is  termed  the  optic  normal,  b. 

Crystals  are  said  to  be  optically  positive  or  negative,  depending  upon 
whether  the  acute  bisectrix  is  the  vibration  direction  of  the  slow  or 
fast  rays,  c  or  a  respectively.  The  direction  of  the  optic  normal  is 
commonly  designated  as  b. 

Behavior  of  Biaxial  Crystals. — A.  In  Parallel  Polarized  Light  with 
Crossed  Nicols  (a)  Any  Section. — All  sections  of  biaxial  crystals,  with  the 
exception  of  those  perpendicular  to  an  optic  axis,  are  four  times  light 
and  four  times  dark  during  a  complete  rotation  of  the  stage.  The 
extinction  may  be  either  parallel,  symmetrical,  or  inclined  to  an  edge 
or  crack  of  the  crystal  or  section  (Figs.  340,  341  and  352).  In  the  case 
of  orthorhombic  substances,  the  extinction  is  either 
parallel  or  symmetrical.  Monoclinic  substances  possess 
both  parallel  and  inclined  extinctions;  that  is,  sections 
parallel  to  the  b  axis  have  parallel  extinction,  while  all 
other  sections  have  inclined  or  oblique  extinction. 
Maximum  obliquity  is  observed  on  sections  perpen- 
dicular to  the  6  axis  In  triclinic  substances  all  extinc-  j^0  352 
tions  are  inclined. 

(b)  Sections  Perpendicular  to  an  Optic  Axis. — These  sections  do  not 
extinguish  when  the  stage  is  rotated  between  crossed  nicols,  but  remain 
uniformly  illuminated.  In  convergent  light,  an  interference  figure  is 
observed  (see  Fig.  359,  page  119). 

B.  In  Convergent  Polarized  Light  with  Crossed  Nicols  (a)  Sections  Per- 
pendicular  to  the  Acute  Bisectrix,  Bxa. — These  sections  show  an  inter- 
ference figure  consisting  of  two  series  of  oval-like  curves  upon  which  two 
dark  brushes  are  superimposed.  In  the  normal  position,  that  is,  when 
the  plane  including  the  optic  axis  and  the  direction  at  right  angles  to  it 
are  parallel  with  the  cross  hairs,  the  interference  figure  resembles  Fig. 
353.  In  white  light  the  curves  are  colored,  while  in  monochromatic 
light  they  are  alternately  light  and  dark.  The  distance  between  the 
optic  axes  or  "eyes"  gives  some  indication  of  the  size  of  the  angle  of  the 
optic  axes.  The  closer  together  the  "eyes"  are,  the  smaller  is  the  angle 
(Fig.  354)  and  vice  versa.  The  angle  of  the  optic  axes  is  constant  for 
any  given  substance  and  is  independent  of  the  thickness  of  the  section, 
provided  the  temperature  remains  the  same.  From  the  number  of  curves 
in  the  interference  figure,  some  idea  of  the  double  refraction  may  be 
obtained,  for  the  stronger  the  double  refraction  the  larger  the  number 


118  MINERALOGY 

of  the  curves  in  the  field  of  vision,  provided  the  sections  are  of  the 
same  thickness. 

The  optical  properties  of  biaxial  crystals  are  very  complex,  and  only 
an  elementary  and  incomplete  explanation  of  the  formation  of  these  inter- 
ference figures  will  be  given.  The  black  cross  or  hyperbolic  brushes 


FIG.  353.  FIG.  354. 

appear  wherever  the  vibration  directions  of  the  emergent  rays  are  paral- 
lel to  those  of  the  nicols.  At  all  other  points  of  the  section  the  emergent 
rays  have  vibration  directions  which  are  inclined  to  those  of  the  nicols 
and  interference  of  light,  as  explained  on  page  112,  will  therefore  take 


FIG.  355.  FIG.  356. 

place.  As  these  vibration  directions  change  most  rapidly  around  the 
optic  axes,  the  curves  there  will  be  smaller  and  closer  together  than  else- 
where. These  curves  are  unaltered  as  the  stage  is  rotated.  The  dark 
brushes,  however,  change.  Compare  Figs.  355  and  356. 

The  positive  and  negative  character  of  biaxial  crystals  may  be  de- 
termined from  the  interference  figure  by  using  the  mica  or  gypsum  test 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS 


119 


plates,  as  described  on  page  116.  When  the  spots  are  in  the  same  quad- 
rants as  the  marked  directions  on  the  test  plate  (c,  mica;  or  a,  gypsum) 
the  substance  is  negative,  and  positive  in  the  opposite  quadrants. 

(6)  Sections  Inclined  to  the  Acute  Bisectrix,  Bxa. — These  sections  show  a 
partial  interference  figure,  usually  only  one  optic  axis  or  "eye"  and  a 


FIG.  357. 


FIG.  358. 


portion  of  the  brushes  being  visible  (Figs.  357  and  358).     The  brushes 
always  move  in  a  direction  opposite  to  that  of  the  stage. 

(c)  Sections  Perpendicular  to  an  Optic  Axis. — These  sections  show  the 
emergence  of  an  optic  axis,  the  observed  interference  figure  being  il- 
lustrated by  Fig.  359.  This  figure  does  not  remain  stationary  when 


FIG.  359. 

the  stage  is  rotated,  as  is  the  case  with  interference  figures  of  uniaxial 
substances,  page  115. 

(d)  Sections  Parallel  to  the  Plane  of  the  Optic  Axes. — Sections  of  this 
character  do  not  in  general  show  interference  figures,  especially  if  studied 
in  white  light. 


120  MINERALOGY 

(e)  Dispersion  of  the  Optic  Axes,  r  >vorr  <  v. — In  Fig.  356  illustrat- 
ing biaxial  interference  figures,  the  size  of  the  angle  of  the  optic  axes  is 
indicated  by  the  distance  between  the  centers  of  the  eyes.  When 
white  light  is  used  and  the  interference  figures  are  viewed  in  the  45° 
or  diagonal  position,  the  hyperbolic  brushes  show  red  and  blue  or  violet 
fringes.  These  fringes  are  especially  distinct  at  r  and  v  as  shown  in 
Figs.  360  and  361.  This  is  due  to  the  fact  that  the  size  of  the  angle 
of  the  optic  varies  with  the  color.  In  some  cases,  the  angle  for  red  is 
larger  than  for  violet,  and  vice  versa.  If  red  appears  on  the  convex 
side  of  the  hyperbolic  brushes,  it  means  that  the  optic  angle  for  red  is 
larger  than  for  blue  or  violet;  that  is  r  >  v.  On  the  other  hand,  if  violet 
is  observed  on  the  convex  side  of  the  brushes,  the  angle  for  violet  is  the 
larger,  namely  v  >  r.  That  is,  the  dispersion  of  the  optic  axes  is  directly 
opposite  to  what  appears  to  be  the  case  from  the  position  of  the  colors 
in  the  interference  figure.  This  is  due  to  the  fact  that  from  the  white 


r\v 


FIG.  360.  FIG.  361. 

light  travelling  along  the  optic  axes  of  the  various  colors,  certain  com- 
ponents are  eliminated  and  other  intensified.  Hence,  where  the  axes 
for  red  light  emerge,  say  at  r  in  Figs.  360  and  361,  red  will  have  been 
eliminated,  and  the  resultant  light  will  be  violet.  At  v,  violet  has  been 
lost,  and  in  the  interference  figure  red  will  appear  at  the  corresponding 
positions.  The  observations  of  the  character  of  the  dispersion  of  the 
optic  axes  is  best  made  with  the  interference  figure  in  the  diagonal 
position  on  any  section  where  a  portion  of  a  hyperbolic  brush  is  dis- 
tinctly visible  near  the  center  of  the  field.  Dispersion  aids  materially  in 
identifying  biaxial  substances. 

Circular  Polarization. — Some  substances  show  circular  polarization; 
that  is,  they  rotate  the  plane  of  polarization.  The  most  notable  of 
such  substances  among  the  common  minerals  is  quartz.  As  is  well 
know,  quartz  occurs  in  enatiomorphous  crystals;  that  is,  in  right  and 
left  hand  crystals  (see  Figs.  190  and  191,  page  53).  This  type  of  de- 
velopment is  also  observed  on  crystals  of  tartaric  acid,  cane  sugar, 
and  sodium  chlorate.  In  some  particulars,  the  behavior  of  substances 
possessing  circular  polarization  is  unique.  The  effect  of  circular  polariza- 
tion in  uniaxial  crystals  only  will  be  considered. 

A .  Parallel  Polarized  Light  and  Crossed  Nicols  (a)  Sections  Cut  Perpen- 
dicular to  the  c  Axis. — As  the  c  axis  in  these  substances  is  not  an  isotropic 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS  121 

direction,  sections  cut  perpendicular  to  it  do  not  extinguish  between 
crossed  nicols,  but  remain  uniformily  illuminated  when  the  stage  is 
rotated. 

(6)  Sections  cut  parallel  or  inclined  to  the  c  axis.     These  sections 
behave  like  those  described  on  page  115. 


FIG.  362. 

B.  Convergent  Polarized  Light  and  Crossed  Nicols.  Sections  Cut 
Perpendicular  to  the  c  Axis. — An  interference  figure  quite  analogous 
to  the  regular  uniaxial  interference  figure  is  obtained  (Fig.  362).  It 
will  be  observed  that  the  dark  brushes  do  not  extend  entirely  across  the 
center  of  the  figure.  By  rotating  the  upper  nicol,  the  character  of  the 


FIG.  363.  FIG.  364. 

rotation  of  polarization  may  be  determined.  That  is,  whether  it  is  to  the 
right  or  left.  If  the  upper  nicol  is  rotated  in  the  proper  direction,  the  circles 
of  the  figure  enlarge;  but  if  it  is  rotated  in  the  opposite  direction  to  that 
of  the  rotation  of  the  plane  of  polarization,  the  circles  contract.  By 
using  the  mica  test  plate,  a  two-armed  spiral  is  obtained.  The  direction 


122 


MINERALOGY 


of  rotation,  being  indicated  by  the  directions  of  the  arms  (Figs.  363 
and  364).  By  placing  two  sections  of  quartz  of  the  same  thickness 
over  one  another,  a  figure  with  a  four-armed  spiral  results.  These 
are  the  spirals  of  Airy  (Figs.  365  and  366).  The  direction  of  the  arms 
of  the  spirals  indicates  the  character  of  the  rotation  in  the  lower  section. 
Twin  Crystals. — The  fact  that  crystals  are  twinned  is  easily  recog- 
nized in  polarized  light,  especially  if  they  are  anisotropic. 


FIG.  365. 


FIG.  366. 


a.  Polarized  Light  and  Crossed  Nicols. — Anisotropic  crystals  showing 
twinning  do  not  extinguish  uniformly.     Certain  portions  of  the  crystal 
may  be  dark,  while  other  portions  are  light,  when  the  stage  is  rotated. 
Figures  367  and  368  show  the  behavior  of  contact  twins,  and  Fig.  369 
that    of    a   section    with  polysynthetic  twinning.     Obviously,  twinned 
crystals  of  isotropic  substances  will  have  no  effect  upon  polarized  light. 

b.  Convergent  Light  and  Crossed  Nicols. — In  properly  oriented  sections, 
interference  figures  may  be  observed  as  shown  in  Fig.  370. 


FIG.  367" 


FIG.  368.         FIG.  369. 


FIG.  370. 


Pleochroism. — The  absorption  of  light  in  colored  sections  and  crystals 
of  uniaxial  and  biaxial  substances  varies  with  direction.  In  the  case 
of  uniaxial  substances,  there  are  two  principal  colors  for  transmitted 
light.  These  colors  are  obtained  when  the  light  vibrates  either  parallel 
and  perpendicular  to  the  c  axis.  Uniaxial  substances  are  therefore  said 
to  be  dichroic.  In  biaxial  crystals  there  are  three  principal  colors  cor- 


CRYSTALLOGRAPHICAL  OPTICAL  INSTRUMENTS 


123 


responding  to  the  three  principal  optical  directions  at  right  angles  to 
each  other.     Biaxial  substances  are  therefore  trichroic. 

Pleochroism  is  easily  recognized  under  the  microscope  by  first  de- 
termining the  extinction  directions  of  the  section  or  crystal  under  con- 
sideration. Then  bring  one  of  these  directions  parallel  to  the  vibration 
direction  of  the  lower  nicol  or  polarizer.  Now  remove  the  upper  nicol 
and  observe  the  color.  Rotate  the  stage  through  90°  and  note  the  change 
in  color.  Strongly  pleochroic  substances  show  marked  changes  in  color 
when  studied  in  this  way. 

Isotropic  substances,  that  is,  those  which  are  amorphous  or  belong 
to  the  cubic  system,  do  not  show  pleochroism. 

Summary. — Behavior  of  sections,  crystals,  or  fragments  in  parallel  light 
between  crossed  nicols. 

(a)   No  regular  out- 

line,structure,cleav- 

age,  or  etch  figures. 

(6)  Regular  outline, 

structure,  cleavage, 

and  etch  figures. 


All  sections  remain  dark 
through  360°. 


|  Isotropic 


Amorphous 


Cubic 


Not  all  sections  remain 
dark  through  360°.  Some 
are  four  times  light  and 
dark,  others  remain  uni- 
formly light. 


Anisotropic 


(a)  Isotropic  and 
doubly  refractive 
sections.  The  first 
show  an  uniaxial  in- 
terference figure  in 
convergent  light. 


(b)  Sections  either 
extinguish  regularly 
or  remain  uniformly 
light.  The  latter 
show  the  emergence 
of  an  optic  axis  in 
convergent  light. 


Hexagonal.  Isotropic 
sections  are  trigonal 
or  hexagonal  in  out- 
line. 

Tetragonal. 
Isotropic  sections  are 
tetragonal  or     dite- 
tragonal  in  outline. 

Orthorhombic. 
All     sections     show 
parallel  or  symmetri- 
cal extinction. 

Monoclinic. 
Sections  show  paral- 
lel,   symmetrical    or 
inclined  extinction. 

Triclinic. 

All  sections  show  in- 
clined extinction. 


Order   of    Procedure  and    Methods  for    Recording   Observations. 

In  studying  sections,  crystals,  or  fragments  under  the  polarizing  micro- 
scope, the  following  order  for  making  determinations  is  suggested : 

Parallel  Polarized  Light 

1.  Isotropic  or  anisotropic. 

2.  Index  of  refraction;  higher  or  lower  than  Canada  balsam  or  the  liquid  in  which 
substance  is  embedded,  if  in  fragments. 


124 


MINERALOGY 


3.  Outline  of  section  or  crystal.     Cleavage  cracks. 

4.  Extinction    directions — parallel,    symmetrical,   or  inclined.     Measurement    of 
extinction  angles. 

5.  Determination  of  fast  and  slow  rays. 

6.  Order  of  interference  colors.     Double  refraction. 

7.  Pleochroism. 

Convergent  Polarized  Light 

1.  Uniaxial  or  biaxial  figure.     Orientation. 

2.  If  biaxial,  note  size  of  optic  angle. 

3.  Positive  or  negative  character. 

4.  Double  refraction. 

5.  Dispersion. 

6.  Circular  polarization. 

7.  System.     See  summary. 

Figures  371  and  372  indicate  a  very  good  method,  suggested  by 
Weinschenk,  for  recording  the  various  optical  properties  of  substances, 
as  determined  under  the  microscope.  In  both  figures  the  material  repre- 
sented was  in  the  form  of  small  crystals.  The  outline  of  the  substance 


•£jf*^l 

+ 

IB- 

i 

/ 

FIG.  371. 


FIG.  372. 


should  be  sketched  and  important  angles  measured  and  their  sizes  indi- 
cated. The  direction  of  cleavage  cracks  may  be  shown  as  in  figure  371. 
The  various  extinction  directions  are  shown  by  arrows.  The  approxi- 
mate value  of  the  indices  of  refraction  for  these  directions  can  be  indicated 
by  lines  of  different  widths;  that  is,  light  lines  indicate  low  indices,  heavy 
lines  high  indices.  The  strength  of  double  refraction  is  given  by  the  arc 
inclosing  the  vibration  directions,  which  may  be  drawn  light  or  heavy 
in  accordance  with  the  variation  from  weak  to  strong  double  refraction, 
or  one  or  more  arcs  may  be  used.  Pleochroism  is  shown  in  connection 
with  the  vibration  directions,  the  colors  being  designated.  The  location 
of  the  optic  axes,  size  of  the  optic  angle,  and  dispersion  are  all  easily 
indicated. 


CHAPTER  XI 


CHEMICAL  PROPERTIES 

As  indicated  earlier,  minerals  have  a  characteristic  chemical  compo- 
sition; that  is,  when  pure  they  may  be  either  elements  or  chemical  com- 
pounds. If  minerals  are  elements,  the  elements  are  said  to  occur  native. 
We  may  thus  speak  of  native  gold,  native  silver,  and  native  copper.  Ob- 
viously, most  of  the  minerals  are  chemical  compounds. 

Chemical  Formulas. — The  determination  of  the  principal  chemical 
constituents  of  a  mineral  can  frequently  be  made  most  rapidly  by  blow- 
pipe methods.  These  methods  are  discussed  in  detail  in  the  next  chapter. 
The  determination  of  the  quantitative  composition  of  minerals  belongs  to 
the  domain  of  chemistry,  the  usual  methods  of  the  analytical  chemist 
being  employed.  The  formulas  representing  the  chemical  composition 
of  minerals  are  calculated  in  exactly  the  same  way  as  for  any  other  chem- 
ical substance.  For  example,  an  analysis  of  chalcopyrite  from  Mtisen, 
Germany,  gave  Laspayres  the  following  results : 


i  ii 

Analysis,  .      Atomic 

per  cent.  ^weights 

Cu 34.89  -r-  63.57 

Fe 30.04  ^  55.84 

S...      .  34.51  -f-  32.06 


III 

Combining 
Ratios 

0/5488 

0.5379 
1.0767 


IV 

1.020 
1.000 
2.002 


By  dividing  the  percentages  (1)  of  the  vari- 
ous constituents  by  the  atomic  weights  (II)  of 
the  same,  their  combining  ratios  (III)  are  ob- 
tained. These  can  then  be  expressed  in  approxi- 
mate whole  numbers  (IV  and  V),  from  which 
following  ratio  results: — 

Cu  :  Fe  :  S  =  1  :  1  :  2.  .This  gives  CuFeS2  as 
the  formula  for  chalcopyrite. 

In  the  case  of  more  complex  minerals  where 
the  composition  is  indicated  by  giving  the  per- 
centages of  the  various  oxides  present,  the  pro- 
cedure is  the  same,  with  the  exception  that  the 
molecular  weights  of  the  oxides,  that  is,  the  sum  ^j^V^IS 
of  the  atomic  weights  of  the  elements  in  the  in  Yale  University  (1893- 
same,  are  used.  Thus,  Brax  in  analyzing  a  beryl  J^rican 
from  Paavo,  Finland,  obtained  the  following:  eraiogist. 

125 


FIG.  373. — Samuel   L. 


126 


MINERALOGY 


I  II  III  IV 

Analysis,  Molecular  Combining 

per  cent.  weights  Ratios 

SiO2 66.37  -T-         60.3  =       1.1007  =        5.843 

A12O3 19.26  -7-        102.2  =       0.1884  =         1.000 

BeO...         ,    14.01  -f-         25.1  =        0.5619  =.       2.983 


These  oxides  therefore  combine  in  the  following  ratio : 
BeO  :Al2O3:SiO9  =  3:1:6,  from  which  the  formula  3BeO.Al2O3.6SiO2 
or  Be3Al2Si6Oi8  is  obtained. 

Percentage  Composition. — When  the  formula  of  a  mineral  has  been 
established,  it  is  possible  to  calculate  what  percentages  of  the  various  con- 
stituents should  theoretically  be  present.  Indeed,  the  degree  of  purity 
of  a  mineral  may  often  be  easily  estimated  by  comparing  an  analysis  with 
the  theoretical  percentage  composition,  calculated  from  the  generally 
accepted  formula.  Referring  again  to  the  mineral  chalcopyrite,  the  for- 
mula of  which  was  calculated  above  as  CuFeS2,  we  may  determine  its 
theoretical  percentage  composition  by  ascertaining  the  percentage  the 
combining  weight  of  a  given  constituent  is  of  the  molecular  weight  of  the 
mineral  as  a  whole.  Thus, 


Constituents 


Cu.. 


Fe 


Atomic 
weights 


63.57 


55.84 


32.06 


Combining 
ratios 


2 


P: 

Combining 
weights 

63.57 
55.84 
64.12 

roportion  of 
molecular 
weight  of          ( 
mineral 

63.57 

Theoretical 
percentage 
jomposition 

34.64 
30.42 
34.94 

183. 
55 

53 

.84 

183 
64 

53 
12 

183 

.53 

183.53 

(Molecular  weight 
of  minerals) 

100.00 

Using Be3Al2Si6Oi8 as  the  formula  for  beryl,  the  theoretical  percentage 
composition  of  the  various  constituents  may  be  calculated  as  follows : 


Constituents 


SiO, 


A1203 


BeO. 


Molecular 
weights  of 
radicals 

60.3 
102.2 
25.1 

Combining 
ratio 

6 
1 
3 

Combining 
weights  of 
radicals 

361.8 
102.2 

75.3 

Proportion 
of  molecular 
weight  of 
mineral 

361.8 

Theoretical 
percentage 
composition 

=      67.09 

539.3 
102.2 

539.3 
75.3 

—      18.95 
13.96 

539.3 

(Molecular  weigh 
of  mineral) 

539.3 

100.00 

Names. — Although  chemical  names  may  be  assigned  to  minerals,  it  has 
long  been  common  practice  to  designate  them  by  special  or  mineralogical 
names.  These  mineral  names  are  given  for  various  reasons.  In  some 
instances,  as  in  the  case  of  celestite,  the  name  refers  to  the  light  blue  color 


CHEMICAL  PROPERTIES 


127 


h-  1 

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0 

« 

0 

CO        *-l- 

GO        3O 

o  a    t»  n 

O           °2 

• 

, 
Chromium 
Cr  =  52.0 

1  Selenium 
Se  =  79.2 

Molybdenum 
Mo  =  90.0 

1  Tellurium 
Te  -  127.5 

1  • 

O                                                   IQ 

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Ir3         ^t 

c 

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Titanium 
Ti  -  48.1 

Germaniu 
Ge  =  72. 

Zirconium 
Zr  =  90.0 

c 

02 

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Gallium 
i  =  09.9 

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300 

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c 

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1 

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12  13 

Si     8* 
**    II 

Calcium 
Ca  =  40.07 

s: 

Strontium 
Sr  =  87.03 

Cadmiui 
Cd  =  112.4 

Barium 
Ba  =  137.37 

li   s 

l     l     !'   ES 

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a  =3  " 

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tftf 

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128 


MINERALOGY 


which  is  commonly  observed  on  this  mineral.  Azurite  also  has  reference 
to  color,  namely  a  deep  azure  blue;  Vesuvianite  to  Mount  Vesuvius,  where 
first  found,  and  tetrahedrite  to  its  crystallization  in  tetrahedrons.  Argen- 
tite  is  so  called  because  it  is  a  compound  of  silver  (argentum).  Magnesite 
is  a  compound  of  magnesium.  Scheelite  is  named  after  Scheele,  a  Swed- 
ish chemist,  and  wollastonite  after  Wollaston,  an  English  scientist.  It  is 
thus  seen  that  is  some  instances,  outstanding  physical  or  chemical  prop- 
erties have  been  incorporated  in  the  names,  whereas  in  other  cases  the 
minerals  have  been  named  after  distinguished 
scientists  or  after  the  locality  where  first  found. 
Isomorphism. — It  can  be  easily  shown  that 
the  various  properties  of  minerals  vary  in  general 
with  the  chemical  composition.  In  order  to  em- 
phasize this,  it  will  be  well  to  review  briefly  the 
periodic  system  of  chemical  elements.  In  1869 
the  Russian  chemist  Mendeleeff  published  a 
classification  of  elements  in  which  they  were 
arranged  in  order  of  their  increasing  atomic 
weights.  This  classification  is  given  on  page 
127.  After  certain  intervals  or  periods,  elements 
are  observed  which  possess  similar  properties. 
For  example,  in  group  II  calcium,  strontium, 
and  barium,  are  found  directly  under  one 
another.  These  elements  are  extremely  closely 
related  to  each  other  chemically.  Obviously 
then,  the  carbonates  of  these  three  elements, 
CaC03,  SrCO3,  and  BaC03,  will  possess  strik- 
ingly similar  chemical  properties.  These  carbonates  occur  in  nature 
as  the  minerals  aragonite,  strontianite,  and  witherite,  respectively.  They 
all  crystallize  in  the  orthorhombic  system. 

The  following  tabulation  gives  the  molecular  weights,  the  specific 
gravities,  several  important  angles,  and  the  elements  of  crystallization 
of  the  minerals  aragonite,  strontianite,  and  witherite. 


FIG.  374.— Paul  H.  von 
Groth  (1843  — ).  Professor 
of  crystallography  and  min- 
eralogy in  the  University  of 
Munich.  Eminent  for  his 
contributions  on  chemical 
and  physical  crystallog- 
raphy. 


Formula 

Molecular 
weights 

Specific 
gravity 

Angles 

Elements  of  crystallization 

Prism 

Dome 

a 

b 

c 

Aragonite 
CaCO3  

100.0 
147.6 
197.4 

2.9 
3.7 
4.3 

63°   48' 

62°  41' 
62°  12' 

71°  33' 
71°  48' 
72°  16' 

0.6228 
0.6089 
0.5949 

:  1  : 
:  1  : 
:  1  : 

0.7204 
0.7237 
0.7413 

Strontianite 
SrSO3  
Witherite 
BaCO3  

It  is  observed  that  the  specific  gravities  increase  regularly  with  the 


CHEMICAL  PROPERTIES  1  29 

molecular  weights.  The  size  of  corresponding  prism  and  dome  angles 
on  crystals  of  these  three  minerals  is  of  the  same  character.  A  close 
examination,  however,  reveals  small  but  regular  differences.  This  is 
also  true  of  the  elements  of  crystallization.  In  both  cases,  nevertheless, 
the  fact  that  the  values,  although  among  themselves  slightly  different, 
are  of  the  same  order,  is  at  once  noticed. 

Substances  with  analogous  chemical  compositions  which  crystallize 
in  forms  that  are  strikingly  similar  are  said  to  be  isomorphous.  Such 
substances  may  also  crystallize  together,  that  is,  an  analysis  of  stronti- 
anite  will  not  infrequently  show  the  presence  of  considerable  calcium 
and  barium  replacing  the  strontium.  Indeed,  there  are  a  number  of 
instances  where  two  chemical  compounds  may  crystallize  together  in 
varying  proportions.  A  striking  illustration  is  the  plagioclase  series  of 
feldspars  in  which  albite,  NaAlSi3O8,  and  anorthite,  CaAl2Si2O8,  are  the 
end  members.  Between  them  are  intermediate  members  whose  compo- 
sition and  properties  vary  regularly  from  that  of  albite  on  the  one  hand 
to  that  of  anorthite  on  the  other.  This  is  clearly  shown  by  the^  follow- 
ing table: 

Albite,         NaAlSi3O8  ...................................  (Ab) 

Oligoclase,  Ab  .................  ..................  Ab3Ani 

Andesine,         Ab3Ani  ...................................  AbiAni 

Labradorite,    AbiAni  ...................................  AbiAn3 

Bytownite,       AbiAn3  ...................................  An 

Anorthite,  CaAl2Si2Os  ....................................  (An) 

Isomorphism  is  one  of  the  most  important  principles  in  chemical 
mineralogy,  for  only  in  rare  instances  are  minerals  absolutely  pure. 
Usually,  as  already  indicated,  one  or  more  of  the  constituents  have  been 
replaced  by  others  of  analogous  character.  Thus,  in  the  case  of  the 
garnet  group,  the  general  composition  is  best  expressed  by  the  formula 
R"3  R'"2(SiO4)  3.  In  this  formula,  R"  may  be  either  calcium,  magnesium, 
ferrous  iron,  or  manganese.  R"'  indicates  ferric  iron,  aluminum,  or 
chromium.  Usually  one  of  the  elements  in  each  of  these  groups  pre- 
dominates, the  others  being  present  in  varying  amounts.  It  is  common 
practice  to  differentiate  six  distinct  varieties  of  garnet  depending  upon 
the  elements  which  predominate,  as  shown  in  the  following  table: 


Grossularite  ...............  .  ...................... 

Pyrope  ..........................................  Mg3Al2(SiO4)3 

Spessartite  .......................................  Mn3Al2(SiO4)3 

Almandite  .......................................  Fe3Al2(SiO4)3 

Uvarovite  ........................................  Ca3Cr2(SiO4)s 

Andradite  ........................................  Ca3Fe2(SiO4)3 

Between  these  compositions  there  are  all  possible  gradations,  but  in 
every  instance  the  composition  can  be  referred  to  general  formula,  R"sR'"2 
(Si04), 


130  MINERALOGY 

Dimorphism. — Some  chemical  substances  occur  in  different  modifica- 
tions with  distinct  physical  and  chemical  properties.  Thus,  calcium 
carbonate  is  found  in  nature  as  the  minerals  calcite  and  aragonite.  The 
following  table  gives  the  common  characteristics  of  each. 

Name  Crystallization  Specific  Hardness  Optical 

gravity  Character 

/Calcite  Hexagonal  2.7  3  Uniaxial 

CaCO3  <^ 

^Aragonite      Orthorhombic  2.9-3  3.5-4  Biaxial 

When  a  chemical  substance  occurs  in  two  distinct  modifications,  it  is 
said  to  be  dimorphous;  in  three  modifications,  trimorphous;  in  many, 
polymorphous.  Among  the  minerals,  carbon  as  the  diamond  and  graph- 
ite, FeS2  as  pyrite  and  marcasite,  and  KAlSi3O8  as  orthoclase  and  micro- 
cline  are  good  examples  of  dimorphism.  TiO2  is  trimorphous,  for  it 
occurs  as  the  minerals  rutile,  brookite,  and  anatase.  The  element  sul- 
phur is  an  excellent  example  of  a  polymorphous  substance  having  at 
least  six  modifications. 

Isodimorphism. — The  various  members  of  an  isomorphous  series  may 
each  be  dimorphous.  This  is  illustrated  by  the  following  isodimor- 
phous  series. 

Cubic  modification  Compound  Orthorhombic  modification 

Pyrite  FeS,  Marcasite 

Smaltite  CoAs2  Safflorite 

Chloanthite  NiAs2  Rammelsbergite 

If  this  series  is  studied  vertically  the  members  are  seen  to  be  isomor- 
phous, and  when  considered  horizontally  they  are  dimorphous. 


CHAPTER     XII 
FORMATION  AND  OCCURRENCE  OF  MINERALS 

In  general  minerals  may  have  been  formed  in  four  ways : 

1.  From  solution. 

2.  From  fusion. 

3.  By  sublimation. 

4.  By  metamorphism. 

Of  these  methods,  formation  from  solution  and  fusion  are  the  most 
important.  Most  of  the  best  crystals  observed  on  minerals  are  the  result 
of  solidification  from  solution. 

FORMATION  FROM  SOLUTION 

Minerals  may  form  from  solution  in  various  ways.  The  following 
are  some  of  the  most  important  methods. 

(a)  Evaporation  of  the  Solvent. — Gypsum  and  halite  are  commonly  the 
result  of  the  simple  evaporation  of  the  solution  in  which  they  were  dis- 
solved. In  many  instances  these  deposits  are  of  great  thickness.  This  is 
especially  true  of  those  occurring  in  central  New  York,  Michigan,  Kansas, 
and  Iowa.  Many  minerals  have  been  formed  in  this  way. 

(6)  Loss  of  Gases  Acting  as  Solvents. — When  water  containing  a  con- 
siderable amount  of  carbon  dioxide  in  solution  comes  in  contact  with 
limestone,  calcium  carbonate  readily  passes  into  solution  as  the  acid  or 
bicarbonate  (CaH2(CQ3)2).  This  is,  however,  an  unstable  compound  and 
due  to  various  factors,  the  carbon  dioxide  in  solution  may  be  lost  causing 
the  bicarbonate  to  revert  to  the  insoluble  normal  carbonate  (CaC03), 
which  is  at  once  deposited.  In  limestone  districts  calcium  carbonate  is 
thus  frequently  dissolved  in  large  quantities  and  subsequently  deposited 
in  caves  in  the  form  of  stalactites^  suspended  from  the  roof,  or  as  stalag- 
mites, found  upon  the  floor  of  the  caves.  It  is  also  frequently  deposited 
in  this  way  around  springs  and  in  the  beds  of  the  streams  resulting  from 
them.  Here  it  is  generally  observed  as  moss-like  deposits,  often  en- 
closing twigs  and  leaves,  and  is  called  calcareous  tufa  or  travertine.  By 
virtue  of  the  presence  of  carbon  dioxide,  calcium  carbonate  passed  into 
-  solution  but  was  later  deposited  when  the  carbon  dioxide  escaped. 

(c)  Change  of  Temperature  and  Pressure. — In  regions  of  geysers  and 
hot  springs  the  solubility  of  the  circulating  water  is  commonly  greatly 
increased  because  of  its  high  temperature  and  the  pressure  to  which  it  is 

131 


132  MINERALOGY 

subjected.  These  waters  therefore  frequently  contain  much  more  min- 
eral matter  in  solution  than  can  be  retained  after  they  reach  the  surface, 
where  the  temperature  is  lowered  and  the  pressure  reduced.  In  these 
localities  considerable  quantities  of  silicious  sinter  or  geyserite  are  ob- 
served, which  have  formed  in  this  way. 

(d)  Interaction  of  Solutions. — As  is  commonly  observed  in  the  chem- 
ical laboratory,  two  solutions  may  interact  and  form  an  insoluble  com- 
pound ^ich  is  at  once  precipitated  or  deposited.     Thus,  a  solution  of 
calcium  sulphate  (CaSO4)  when  brought  into  contact  with  one  of  a  soluble 
barium  compound  such  as,  BaCl2,  yields  at  once  the  insoluble  barium 
sulphate  (BaSO4).     When  found  in  nature,  barium  sulphate  is  called 
barite.     This  mineral  has  undoubtedly  been  frequently  formed  in  this 
way. 

(e)  Interaction  of  Solutions  and  Solids. — A  solution  containing  lead 
and  sulphur  ions  may  interact  with  limestone  and  yield  galena  (PbS), 
calcite  or  calcium  carbonate  having  passing  into  solution.     Thus,  galena 
replaces  the   calcite  of   the  limestone.     This  process  is  often    called 
replacement  or  metasomatism.     In  the  same  way  the  interaction  of  a  solu- 
tion of  zinc  sulphate  with  limestone  may  cause  the  formaton  of  smith- 
sonite  (ZnCO3)  and  calcium  sulphate.     Metasomatism  has  often  been  of 
great  importance  in  the  formation  of  valuable  ore  deposits. 

(/)  Interaction  of  Gases  with  Solutions. — Waters  charged  with  hydro- 
gen sulphide  precipitate  sulphides  from  mine  and  quarry  waters  contain- 
ing copper  or  iron.  Presumably,  many  of  the  sulphide  minerals  have 
thus  been  formed. 

(g)  Action  of  Organisms  upon  Solutions. — Mollusks,  corals,  crinoids, 
and  other  organisms  secrete  calcium  carbonate  from  ocean  water  in  the 
formation  of  shells  and  the  hard  parts  of  their  bodies.  This  calcium 
carbonate  may  be  either  in  the  form  of  calcite  or  aragonite.  Sponges, 
radiolaria,  and  diatoms  similarly  secrete  silica.  Diatomaceous  earth, 
chert,  and  other  forms  of  chalcedony  may  be  formed  in  this  manner. 
Limonite  and  sulphur  may  result  from  the  action  of  certain  bacteria  upon 
water  containing  iron  or  sulphates  in  solution.  Algae  may  cause  the 
deposition  of  gyserite  from  the  water  of  hot  springs.  The  large  deposits 
of  soda  niter  in  Chile  are  thought  by  some  to  be  the  result  of  the  action 
of 'organisms. 

FUSION 

The  minerals  composing  the  igneous  rocks  are  the  result  of  solidi- 
fication from  a  molten  mass  called  the  magma.  Only  rarely,  however, 
does  such  a  molten  mass  contain  the  constituents  of  a  single  mineral,  so 
that  generally  several  minerals  are  formed  on  cooling.  In  reality  solidi- 
fication takes  place  from  a  solution  possessing  a  very  high  temperature, 


FORMATION  AND  OCCURRENCE  OF  MINERALS  133 

and  obviously  good  crystals  can  only  result  if  the  process  of  cooling  is 
comparatively  slow.  Hence,  some  portion  of  the  molten  or  fused  mass 
is  apt  to  form  amorphous  and  glassy  material.  Water  and  other  active 
mineralizers  are  frequently  contained  in  the  magma  and  are  of  great 
importance  in  determining  the  character  and  size  of  the  result  ing  minerals. 
Such  igneous  rocks  as  granite,  syenite,  diorite,  and  basalt,  for  example, 
are  composed  of  minerals  formed  in  this  way.  For  a  further  description 
of  the  character  and  composition  of  such  rocks,  see  pages  137  and  143. 

SUBLIMATION 

Under  this  heading  are  included  not  only  the  minerals,  which  are 
the  result  of  having  passed  from  a  solid  state  through  the  vapor  and  back 
to  the  solid  state  again,  but  also  those  which  are  the  result  of  the  inter- 
action of  gases  upon  another  and  upon  the  country  rock.  Halite  (NaCl) 
and  sal-ammoniac  (NH4C1)  are  sometimes  the  result  of  simple  sublima- 
tion. In  the  vicinity  of  volcanoes  small  scales  of  hematite  (Fe2O3)  are 
frequently  found  in  the  cavities  of  lava,  resulting  from  the  interaction 
of  volatile  FeCl3  and  water  vapor.  Thus,  2FeCl3  +  3H2O=  Fe2O3  + 
6HC1. 

Among  the  important  volatile  mineralizers,  mention  may  be  made  of 
water  vapor,  which  usually  predominates,  chlorine,  boron,  fluorine,  and 
some  of  their  compounds.  Minerals  formed  in  this  way  are  usually  said 
to  be  the  result  of  pneumatolytic  action  or  pneumatolysis.  One  of  the 
most  prominent  examples  of  this  character  is  the  formation  of  cassiterite 
(SnO2),  which  is  frequently  associated  with  fluorite  (CaF2). 

SnF4  +  2H2O  =  Sn02  +  4HF 

(Cassiterite)  ^ 

4HF  +  2CaCO3  =  2CaF2  +  2H2O  +  2CO2 

(Limestone  (Fluorite) 

or  calcite) 

In  this  case,  it  is  assumed  that  volatile  SnF4  and  water  vapor  interact 
and  form  SnO2  (cassiterite)  and  hj^drofluoric  acid.  The  latter,  however, 
is  an  exceedingly  active  chemical  compound  and  hence  tends  to  react 
with  whatever  it  comes  in  contact,  which  in  the  above  reaction  is  supposed 
to  be  limestone  or  the  calcite  of  the  adjacent  rock.  Fluorite  is  thus 
formed  as  the  result  of  this  reaction. 

The  following  minerals  are  frequently  regarded  as  being  the  result 
of  pneumatolytic  action:  tourmaline,  fluorite,  cassiterite,  topaz,  scapo- 
lite,  and  phlogopite. 

METAMORPHISM 

Under  the  influence  of  certain  processes  involving  principally  heat, 
moisture,  pressure,  and  the  presence  of  alkaline  substances,  profound 
changes  in  the  character,  structure,  and  mineral  constituents  of  rocks 


134  MINERALOGY 

are  frequently  wrought.  In  this  way  sedimentary-  and  igneous 
rocks  may  be  changed.  When  such  changes  are  limited  in  extent,  the 
results  constitute  what  is  commonly  called  local  or  contact  metamorphism. 
This  type  of  metamorphism  is  most  pronounced  in  the  vicinity  of  dikes, 
intrusive  sheets,  and  lava  streams,  that  is,  wherever  older  rocks,  espe- 
cially limestones  and  shales,  have  been  subjected  to  the  action  of  magmas. 
Similar  changes  may,  however,  take  place  over  large  areas,  due  to  what 
are  generally  known  as  mountain-making  processes.  Such  changes 
generally  are  the  result  of  regional  metamorphism. 

a.  Local  or  Contact  Metamorphism. — -A  considerable  number  of  minerals 
are  commonly  the  result  of  contact  metamorphism.  Wollastonite, 
garnet,  graphite,  calcite,  and  diopside  are  frequently  formed  when  im- 
pure limestone  is  metamorphosed  by  contact  action.  If  considerable 
amounts  of  magnesium  are  present  tremolite,  spinel,  phlogopite,  chon- 
drodite,  and  olivine  may  be  formed  in  addition  to  calcite  and  dolomite. 


FIG.  375.— Disseminated  crystals  FIG.    376.— Attached   crystal 

of  orthoclase  in  trachyte.  of  quartz. 

b.  Regional  Metamorphism. — Here  large  areas  have  been  affected, 
and  the  structure  of  the  rocks  may  be  profoundly  changed.  This  type 
of  metamorphism  is,  however,  not  as  productive  of  new  minerals  as  is 
local  or  contact  metamorphism.  By  regional  metamorphism,  soft  or 
bituminous  coal  has  been  changed  to  hard  or  anthracite  coal,  sedimentary 
limestone  to  marble,  and  igneous  granite  to  a  gneiss.  Sandstone  is 
converted  into  quartzite  and  shale  into  slate. 


OCCURRENCE  OF  MINERALS 

Minerals  may  be  found  either  disseminated  throughout  other  minerals 
or  rocks  (Fig.  375)  or  they  may  occur  attached  as  crystals  (Fig.  376) 
or  adhering  as  crusts  or  in  layers  on  other  minerals  or  rocks.  When 
found  disseminated  they  sometimes  exhibit  crystal  forms,  although 


FORMATION  AND  OCCURRENCE  OF  MINERALS 


135 


they  are  most  frequently  observed  in  irregular  particles  or  grains.  Dis- 
seminated crystals  are  generally  doubly  or  fully  terminated.  Crusts  of 
compact  calcite  so  commonly  observed  coating  the  exposed  surfaces  of 
limestone  in  cracks  or  coating  pebbles  in  stream  beds  are  illustrative  of 


FIG.  377.— Vein    of 
serpentine. 


FIG.  378. — Banded  vein  of  sphale- 
rite (dark),  fluorite,  and  calcite. 


the  attached  occurrence.  Under  favorable  conditions  crystals  frequently 
form  with  one  end  well  developed  and  the  other  adhering  to  the  rock  or 
mineral  on  which  it  was  formed.  Attached  crystals  ar°  generally  only 
singly  terminated  (Fig.  376). 


FIG.  379. — Quartz  vein  with 
copper  (dark). 


FIG.  380.— Vein  of  smal- 
tite  and  calcite  (light). 


Cracks  or  crevices  filled  with  mineral  matter,  are  spoken  of  as  veins, 
(Fig.  377).  When  a  vein  consists  of  several  minerals  deposited  in 
layers  or  bands,  it  is  termed  a  banded  vein,  (Fig.  378).  Veins  may 
be  symmetrically  or  unsymmetrically  banded,  depending  upon  whether  or 
not  the  same  minerals  are  encountered  in  passing  from  opposite  walls 


136 


MINERALOGY 


of  the  vein  to  the  center  of  it.  The  character  of  veins,  as  to  their  width 
and  constituents,  varies  greatly  in  different  localities.  In  some  instances 
the  width  and  mineral  contents  will  continue  practically  unchanged  over 
considerable  distances  laterally  and  vertically,  whereas  in  other  cases 
marked  changes  take  place  (Figs.  379  and  380).  When  a  vein  consists 
principally  of  unimportant  or  valueless  material,  which  however  contains 
some  mineral  of  value  disseminated  throughout  it,  the  former  is  spoken 
of  as  the  gangue.  Thus,  in  a  gold-bearing  quartz  vein,  quartz  is  obvi- 
ously the  gangue  mineral,  also  see  Figs.  379  and  380. 

Veins  have  been  formed  principally  as  the  result  of  solidification 
of  mineral  matter  from  solution.  These  solutions  may  have  been  de- 
scending or  ascending  in  character,  while  in  some  instances  their  flow  may 
have  been  largely  lateral.  Where  veins  trending  in  different  directions 
cross,  due  to  a  possible  difference  in  the  character  of  the  solutions  from 
which  they  were  formed,  mineralization  is  usually  most  pronounced.  In 


FIG.  381. — Quartz  geode. 

fact,  it  is  well  known  that  the  richest  mineral  deposits,  or  what  are  fre- 
quently called  bonanza  ores,  are  to  be  expected  at  the  intersection  of 
veins. 

Geodes  are  cavities  lined  with  mineral  matter,  which  frequently  con- 
sist of  well-developed  crystals.  Quartz  and  calcite  geodes  are  not 
uncommon  (Fig.  381).  Some  geodes  are  large  enough  to  be  designated 
as  caves.  Thus,  the  "crystal"  cave  on  the  island  of  Put-in-Bay  in  Lake 
Erie  is  a  huge  geode  containing  crystals  of  celestite  (SrSO4).  Similarly, 
large  geodes  lined  with  quartz  crystals  are  found  in  the  Alps  of  Switzerland. 

When  crystals  or  minerals  are  found  in  the  places  they  were  formed,  we 
may  speak  of  them  as  occurring  in  situ.  They  are  also  said  to  be  found 
in  the  parent  or  mother  rock.  When  found  in  the  sands  and  gravels 
of  streams  or  of  other  bodies  of  water,  as  the  result  of  transportation, 
they  are  said  to  occur  in  secondary  deposits  or  placers.  When  gold  is  found 
in  a  quartz  vein,  it  may  be  said  to  be  observed  in  situ}  but  when  it  is 


FORMATION  A  ND  OCCURRENCE  OF  MINERALS  137 

recovered  from  the  sands  and  gravels  of  a  stream  or  lake,  we  refer  to  it 
as  placer  gold.     There  are  also  platinum,  diamond,  and  cassiterite  placers. 

ROCKS 

As  was  indicated  on  page  xii,  the  earth's  crust  consists  of  solid  ma- 
terial, commonly  called  rocks,  and  as  these  are  composed  of  minerals, 
it  is  obvious  that  rocks  must  be  the  source  of  most  minerals.  A  brief 
description  of  the  most  common  and  important  rocks  will  therefore  be 
given. 

Any  mineral  or  aggregate  of  minerals  comprising  an  important  part 
of  the  earth's  crust  may  be  termed  a  rock.  A  rock  may  consist  of  a 
single  component  as,  for  example,  a  sandstone  or  limestone,  see  page  xii. 
In  the  majority  of  rocks,  however,  two  or  more  minerals  are  present  as  is 
illustrated  in  the  case  of  the  granite  where  the  three  principal  constituents 
are  quartz,  orthoclase,  and  mica  or  hornblende.  To  illustrate  the  rela- 
tionship between  minerals  and  rocks,  the  minerals  might  be  compared  to 
the  letters  of  the  alphabet  and  the  rocks  to  the  words. 

Depending  upon  origin  three  main  groups  of  rocks  may  be  differ- 
entiated. The  igneous  rocks  are  those  which  have  resulted  from  the 
solidification  of  a  molten  mass,  commonly  called  a  magma.  The  sedi- 
mentary rocks,  on  the  other  hand,  were  deposited  in  water,  either  as 
fragments  carried  mechanically  or  as  chemical  precipitates,  while  the 
metamorphic  rocks  were  developed  from  either  the  igneous  or  sedimentary 
types  by  geological  forces  including  heat,  pressure,  and  circulating  waters. 

Igneous  Rocks 

If  the  magma  be  permitted  to  cool  slowly  it  will  in  time  become  super- 
saturated with  reference  to  certain  chemical  compounds  which  then 
separate  or  crystallize  out  to  form  the  various  minerals.  The  impor- 
tant rock-forming  minerals  of  igneous  rocks  comprise  (a)  the  essential 
and  (6)  the  accessory  minerals.  The  former  are  those  whose  presence 
have  a  direct  influence  upon  the  character  and  name  of  the  rock.  This 
division  would  include  the  feldspars,  pyroxenes,  amphiboles,  micas,  nephe- 
lite,  leucite,  olivine,  and  quartz.  The  accessory  minerals,  as  the  name 
indicates,  are  those  present  in  smaller  amounts.  They  do  not  affect 
appreciably  the  character  of  the  rock.  The  more  important  ones  would 
include  magnetite,  ilmenite,  pyrite,  pyrrhotite,  apatite,  zircon,  and 
titanite. 

The  order  of  crystallization  from  the  magma,  while  not  constant  in 
all  cases,  tends  to  proceed  in  a  more  or  less  definite  manner.  The  acces- 
sory minerals  being  the  first  to  form,  usually  show  very  good  crystal  out- 
lines. The  ferro-magnesium  minerals  (biotite,  hornblende,  or  augite) 


138 


MINERALOGY 


follow  the  accessory  constituents  and  these  in  turn  are  followed  by  the 
feldspars.  If  the  original  magma  contained  a  large  amount  of  silica, 
the  excess,  if  any  remains  after  combining  to  form  the  above  mentioned 
minerals,  separates  out  as  quartz.  From  this  sequence  it  will  be  seen 
that  the  more  basic  minerals — those  low  in  silica — crystallize  out  first  to 
be  followed  by  those  more  acid  in  composition. 

Those  igneous  rocks  which  are  the  result  of  magmas  that  have  reached 
the  surface  are  termed  extrusive  or  volcanic.  Due  to  the  escape  of 
dissolved  gases  and  the  rapid  rate  of  cooling,  rocks  of  this  type  are  charac- 
terized by  glassy,  cellular,  or  extremely  fine  grained  (felsitic)  textures. 
Magmas,  on  the,  other  hand,  that  have  solidified  at  depths  produce  rocks 

that  are  spoken  of  as  plutonic  or  intrusive. 
These  have  cooled  very  slowly  and  conse- 
quently possess  larger  and  better  developed 
crystal  grains.  They  are  said  to  have  a 
granular  texture.  In  many  instances  the 
texture  of  an  intrusive  rock  is  sufficiently 
coarse  to  permit  of  the  identification  of  all 
the  essential  minerals  with  the  naked  eye. 

The  field  classification  of  igneous  rocks  is 
based    primarily   upon    grain   or   texture   and 
mineral    composition.       The    latter    depends, 
however,  upon  the    chemical    composition    of 
the  original  magma.     Magmas  containing  65 
FIG.  382.— Auguste    to  80  per  cent,  of  SiO2  will  produce  acid  or 
Michel-Levy  (1844-1 911).    light  colored  rocks.     In  these  there  is  devel- 

For    many     years    professor  ,  ,          ,  <,         ,        , 

in  the  College  de  France,  °Ped  an  abundance  of  orthoclase,  some  quartz, 
Paris.  Distinguished  for  his  ancj  a  subordinate  amount  of  ferro-magnesium 

researches    on    rock-forming          .  ,          „,  ,  .         . 

and  synthetic  minerals.  minerals.     Examples  of  this  type  are  granite, 

rhyolite,  aplite,  and  pegmatite.     The  basic  or 

dark  colored  rocks  result  from  magmas  containing  less  than  52  per  cent, 
of  SiO2.  In  these  we  have  an  excess  of  the  ferro-magnesium  minerals, 
some  feldspar  (plagioclase),  and  olivine,  but  no  quartz.  Gabbro,  peri- 
dotite,  pyroxenite,  and  basalt  are  a  few  examples  of  basic  rocks.  The 
intermediate  types  must  then  result  from  those  magmas  whose  Si02 
content  is  somewhere  between  65  and  52  per  cent,  and  are  represented 
by  syenite,  diorite,  trachyte,  and  andesite.  A  summary  of  some  of  the 
more  important  igneous  rocks  is  given  in  the  following  table.  It  should 
be  noted,  however,  that  in  nature  rocks  grade  gradually  from  one  type 
into  another,  and  do  not  show  the  sharp  distinctions  inferred  from  the 
rulings  in  the  diagram. 

From  an  inspection  of  the  chart  it  will  be  seen  that  a  rock  with 
a  granular  texture  is  called  a  granite  when  it  contains  orthoclase,  a 
dark  constituent,  and  quartz,  while  a  rock  with  the  same  texture  without 


FORMATION  AND  OCCURRENCE  OF  MINERALS 


139 


Orthoclase 
acid                          <  

Plagioclase 
intermediate             —  > 

Feldspar-free 
basic 

Dark  constituent 

Mica  or  hornblende 

Hornblende  or  augite 

Augite  or  hornblende 

Distinguishing  mineral. 

-f-  Quartz 

—  Quartz 

—  Quartz        +  Olivine 

—  Olivine 

-1-  Olivine 

Granular  texture 

Granite 

Syenite 

Diorite            Gabbro 
Dolerite 

Pyroxenite 

Peridotite 

Felsitic  texture 

Rhyolite 
Fel 

Trachyte 
site 

Andesite         Basalt 

Augitite 

Limburgite 

Glassy  texture 

Obsidian 
Pitchstone 

Tachylyte 
(Basaltic  glass) 

Cellular  texture 

Pumice 

Sco-ia 

the  quartz  is  known  as  a  syenite.  Rhyolite  and  trachyte  are  mineral- 
ogically  the  equivalents  of  granite  and  syenite  but  possess  a  felsitic 
rather  than  granular  texture.  Diorite,  on  the  other  hand,  is  a  granular 
rock  consisting  essentially  of  plagioclase  and  hornblende,  while  gabbro 
contains  plagioclase,  augite,  and  frequently  some  olivine.  The  term 
dolerite  may  be  employed  for  those  types  of  diorite-gabbro  rocks  where 
it  is  impossible  to  determine  with  the  naked  eye  whether  the  dark  con- 
stituent is  hornblende  or  augite.  Andesite  and  basalt  are  the  felsitic 
equivalents  of  diorite  and  gabbro,  respectively. 

Dike  Rocks. — Frequently  penetrating  the  larger  rock  bodies  will  be 
found  fissures  containing  intrusions  of  igneous  material.  These  occur- 
rences are  known  as  dikes.  They  are  of  later  origin  than  the  rock  pene- 
trated and  may  be  either  extremely  acid  or  very  basic  in  character.  The 
acid  or  light  colored  dikes  include  aplite  and  pegmatite,  while  the  general 
term  lamprophyre  has  been  suggested  for  all  the  basic  types.  Aplite  is 
an  extremely  fine  and  even-grained  rock  consisting  largely  of  quartz 
and  orthoclase  with  a  very  subordinate  amount  of  dark  material.  Peg- 
matite, while  possessing  in  general  the  same  mineral  composition  as  the 
aplite,  has,  on  the  contrary,  an  exceedingly  coarse  and  uneven  texture. 
In  the  formation  of  pegmatites  it  is  believed  that  mineralizers  have  played 
an  important  role.  The  dissolved  vapors  would  not  only  increase  the 
fluidity  of  the  magma,  thus  reducing  internal  friction,  and  permit  the 
growth  of  crystals  of  unusual  size,  but  also  explain  the  size  and  concen- 
tration of  accessory  minerals  which  are  so  abundant  in  some  pegmatites. 
A  list  of  a  few  of  the  more  common  accessory  minerals  would  include  tour- 
maline, beryl,  topaz,  fluorite,  spodumene,  wolframite,  and  columbite. 
The  basic  dikes  are  not  so  well  crystallized  nor  do  they,  as  a  rule,  contain 
the  wealth  of  accessory  minerals  which  characterizes  the  acid  types. 


140  MINERALOGY 

Sedimentary  Rocks 

These  are  all  of  secondary  origin  having  been  derived  from  the  dis- 
integration of  older  rocks  through  the  action  of  agencies  included  under 
the  comprehensive  term  of  " weathering."  That  portion  of  the  mineral 
matter  which  is  carried  away  in  solution  may  at  some  later  period  be 
deposited  either  through  strictly  chemical  action,  by  slow  evaporation,  or 
through  processes  involving  organic  life. 

Sedimentary  rocks  are  characterized  by  a  parallel  or  bedded  structure 
in  which  the  nature  of  the  material  composing  the  layers  varies  in 
thickness,  composition,  and  color  or  size  of  the  individual  grains.  They 
form  widely  extended  deposits  which,  generally  speaking,  are  without 
great  vertical  dimensions,  especially  when  compared  with  some  of  the 
massive  igneous  formations.  A  field  classification  based  on  origin  would 
divide  the  sedimentary  rocks  into  three  main  groups,  (a)  the  mechanical, 
(6)  the  chemical  and  (c)  the  organic  sediments.  The  mechanical  sedi- 
ments would  include  shale,  sandstone,  conglomerate,  and  breccia.  While 
the  formations  of  anhydrite,  gypsum,  and  salt  would  be  classified  as 
chemical  deposits.  Those  of  organic  origin  would  include  coal,  limestone, 
and  dolomite. 

Shale. — The  finest  particles  carried  mechanically  by  the  water,  and 
generally  referred  to  as  mud  or  silt,  when  reaching  the  sea,  settle  quickly 
due  to  the  action  of  the  soluble  salts  in  the  ocean  water.  These  deposits, 
when  consolidated,  yield  a  very  fine  and  even-grained  rock — possessing  a 
good  parting  parallel  to  the  bedding — which  is  known  as  shale.  The 
chief  mineral  components  are  kaolinite,  quartz,  and  feldspar,  although 
these  constituents  cannot  be  distinguished  with  the  naked  eye.  As 
the  amount  of  quartz  and  size  of  the  grain  increases  the  shale  gradually 
passes  over  into  a  sandstone.  The  colors  of  shale  may  vary  from  green 
to  gray  and  in  some  instances  may  even  be  black  (carbonaceous  shale). 
In  some  of  the  shales  of  northwestern  Colorado  and  adjacent  States 
oil  has  been  detected  and  in  several  instances  the  amount  has  reached 
forty  to  fifty  gallons  per  ton  of  rock.  These  are  termed  oil  shales. 
The  oil  can  be  obtained  by  distillation  at  a  low  temperature  and  paraffine 
wax  and  ammonium  sulphate  recovered  from  the  residue. 

Sandstone. — When  particles  of  sand  of  nearly  uniform  size  become 
consolidated  a  sandstone  results.  The  individual  components  are  usually 
rounded  and  consist  essentially  of  quartz.  When  considerable  feldspar 
is  present  the  rock  is  spoken  of  as  feldspathic  sandstone  or  arkose.  The 
cementing  material  varies  greatly  both  in  amount  and  character.  In 
some  instances  it  is  silica,  although  calcium  carbonate,  clay,  or  iron  oxide 
may  serve  as  the  binding  material.  The  most  durable  sandstones  for 
structural  purposes  are  those  with  a  silicious  cement.  Those  containing 
iron  oxide  show,  however,  the  greatest  variation  in  color.  A  thinly 


FORMATION'  AND  OCCURRENCE  OF  MINERALS  141 

bedded  argillaceous  sandstone  is  called  a  flagstone,  while  the  term  freestone 
is  applied  to  those  homogeneous  types  which  occur  in  thick  beds  and  can 
be  worked  in  all  directions  with  equal  ease.  A  conglomerate  is  a  rock  term 
applied  to  rounded,  water  worn  pebbles  of  various  sizes  which  are  held  in 
a  matrix  of  finer  materials.  If  the  fragments  are  sharp  and  angular 
instead  of  rounded  the  term  breccia  is  employed.  Breccias  are  quite 
common  in  limestone  regions  where  the  movement  along  a  fault  plane  has 
crushed  the  rock  to  various  degrees  of  fineness.  These  are  known  as 
friction  breccias  in  contrast  to  volcanic  breccias  which  are  composed  of 
consolidated,  angular  fragments  of  igneous  material. 

Limestone  and  Dolomite. — A  limestone  is  a  sedimentary  rock  consisting 
essentially  of  calcium  carbonate  with  minor  amounts  of  magnesium 
carbonate,  silica,  clay,  iron  oxide,  or  carbonaceous  material.  The  majority 
of  limestones  were  formed  by  organisms  such  as  brachipods,  corals, 
^molluscs,  and  crinoids,  which  have  secreted  calcium  carbonate  taken  from 
the  waters  and  utilized  the  material  to  form  shells  and  skeletons.  The 
pressure  of  superimposed  rocks  has,  in  many  instances,  largely  destroyed 
its  original  fossiliferous  character.  The  variety  known  as  oolitic  limestone 
is  composed  of  small  rounded  grains  of  concretionary  nature.  With  an 
increase  in  the  content  of  magnesium  carbonate,  the  limestone  gradually 
passes  over  to  a  dolomitic  limestone  and  finally  to  a  normal  dolomite, 
which  theoretically  contains  54.35  per  cent.  CaCO3  and  45.65  per  cent. 
MgCO3.  Normal  dolomite  is  both  slightly  heavier  and  harder  than  the 
limestone  and  will  not  effervesce  so  freely  when  treated  with  cold,  dilute 
acids.  Many  dolomites  are  believed  to  be  the  result  of  magnesium 
solutions  reacting  upon  limestones  as  indicated  by  the  equation:  2  CaCO8 
+  MgCl2  =  CaMg(CO3)2  +  CaCl2. 

Metamorphic  Rocks 

The  compressive  force  due  to  contraction  of  the  earth,  together  with 
heat,  caused  by  folding  and  crushing  of  the  rock  strata,  and  the  chemical 
action  of  liquids  produce  profound  changes  in  both  igneous  and  sedi- 
mentary rocks.  The  alterations  noted  are  either  mineralogical  or  chem- 
ical in  character  and  frequently  also  include  a  change  in  the  original 
texture.  The  resultant  rocks,  classified  as  metamorphic,  possess  certain 
features  which  resemble  both  the  igneous  and  sedimentary  types.  They 
are  crystalline  in  character  and  in  this  respect  are  similar  to  the  igneous 
rocks.  Many,  on  the  other  hand,  possess  a  banded  structure  caused  by 
minerals  of  like  character  being  brought  together  in  parallel  layers. 
This  parallel  arrangement  is  termed  schistose  structure.  Some  of  the 
important  "types  referred  to  the  action  of  regional  metamorphism  (page 
134)  include  gneiss,  schists,  quartzite,  slate,  and  marble. 

Gneiss. — This  is  a  laminated  rock  which  generally  has  the  mineral 


142  MINERALOGY 

composition  of  the  granite.  The  intermingled  grains  of  quartz  and 
feldspar  are  separated  by  layers  of  the  dark  constituent.  The  banding 
may  extend  in  straight  parallel  lines  or  be  curved  and  bent.  Gneisses 
differ  from  schists  in  that  they  are  more  coarsely  laminated  and  contain 
the  mineral  feldspar.  They  usually  represent  an  altered  igneous  rock  as 
the  granite,  although  they  may  also  have  originated  from  a  coarse  felds- 
pathic  sandstone  or  conglomerate.  Gneisses  are  of  widespread  occur- 
rence, especially  in  the  older  geological  formations. 

Schists. — These  are  laminated  metamorphic  rocks  which  split  readily 
along  planes  that  are  approximately  parallel.  Depending  upon  the 
character  of  the  prevailing  mineral,  four  types  are  easily  differentiated, 
namely,  the  mica,  chlorite,  talc,  and  hornblende  schists.  In  the  mica 
schist  the  scales  are  so  arranged  that  the  cleavage  directions  are  all 
parallel,  thus  producing  a  rock  of  pronounced  schistose  structure.  In 
addition  to  mica,  more  or  less  quartz,  also  well  developed  crystals  of 
garnet,  cyanite,  and  staurolite  are  frequently  present.  Next  to  the 
gneiss,  the  mica  schist  is  the  most  abundant  metamorphic  rock.  Usually 
it  is  the  result  of  the  alteration  of  a  fine  grained  sedimentary  deposit, 
as  clay  or  shale.  In  chlorite  schist  the  chief  component  is  the  green, 
granular,  or  scaly  mineral  chlorite.  In  many  instances  it  has  been 
formed  from  some  basic  igneous  rock  such  as  gabbro  or  basalt.  In  the 
case  of  talc  schist  the  predominating  mineral  is  talc  which  gives  the  rock 
a  characteristic  soapy  feel.  As  talc  is  a  magnesium  silicate  it  can  only 
be  developed  from  the  feldspar  free  rocks,  or  if  of  sedimentary  origin, 
from  impure  dolomites.  A  schist  consisting  largely  of  black  slender 
prisms  of  hornblende  is  termed  a  hornblende  schist.  As  the  needles  are  all 
arranged  with  their  long  direction  parallel  to  the  schistosity,  these 
schists  cleave  readily  and  show  a  marked  silky  luster. 

Quartzite. — This  is  a  very  firm  compact  rock  containing  quartz  grains 
with  a  silicious  cement.  It  is  the  result  of  the  intense  metamorphism 
of  a  sandstone.  In  an  ordinary  sandstone  it  will  be  seen  that  the  frac- 
ture always  follows  the  cement,  while  in  a  quartzite  it  passes  through 
grains  and  cement  alike. 

Slate. — This  is  an  exceedingly  fine  grained  rock  which  breaks  very 
easily  in  thin  broad  sheets.  The  cleavage,  as  a  rule,  does  not  correspond 
to  the  bedding  planes  of  the  shale  from  which  most  slates  were  derived, 
but  cuts  these  planes  at  various  angles.  In  mineral  composition  the 
slates  consist  of  quartz  and  mica  with  subordinate  amounts  of  chlorite, 
hematite,  or  graphite,  which  contribute  the  green,  red,  and  black  colors, 
respectively.  Slates  containing  a  considerable  amount  of  iron  carbonate 
have  a  tendency  to  discolor  on  exposure  and  are  termed  fading  slates 
in  the  building  trade. 

Marble. — Strictly  speaking,  the  term  marble  includes  limestones  or 
dolomites  which  have  been  recrystallized  and  are  capable  of  taking  a 


FORMATION  AND  OCCURRENCE  OF  MINERALS  143 

polish.  The  term,  however,  is  used  somewhat  loosely  and  not  infre- 
quently includes  any  limestone  that  will  take  a  polish  irrespective  of  its 
crystalline  character.  Scales  of  mica  arranged  in  wavy  streaks  or  bands 
are  frequently  present  which  add  to  the  attractiveness  of  the  stone,  but 
interfere  with  the  continuity  of  the  polish  and  lower  its  resistance  to 
atmospheric  agencies  when  placed  in  exposed  positions.  Marbles  show 
great  variation  in  texture  and  color.  Statuary  marbles  demand  the 
purest  and  whitest  varieties,  while  ornamental  types  show  strongly  con- 
trasted color  effects.  For  structural  purposes  uniformity  of  color  is 
essential.  Marbles  are  not  so  widely  distributed  as  limestones  and  are 
confined  almost  entirely  to  metamorphic  areas. 

DECOMPOSITION  AND  WEATHERING  OF  MINERALS 

As  soon  as  minerals  are  formed  and  are  exposed  to  atmospheric  con- 
ditions, they  are  subject  to  change.  By  the  action  of  moisture,  the  oxy- 
gen of  the  air,  humus  acids  of  the  soil,  and  other  agencies  profound 
changes  are  brought  about.  In  some  cases  the  alteration  takes  place 
rather  rapidly  while  in  others  it  may  proceed  very  slowly.  All  minerals 
are,  however,  sooner  or  later  acted  upon.  The  changes  are  effected  by 
the  action  of  processes  familiar  to  students  of  chemistry.  vSome  of  the 
more  important  are:  solution,  oxidation,  reduction,  hydration,  and 
carbonatization.  In  most  instances  several  of  these  processes  may  have 
been  effective  simultaneously  or  successively. 

PSEUDOMORPHS 

Not  infrequently  minerals  alter  in  such  a  way  that  the  structure  of  the 
original  specimen  is  retained.  For  example,  limonite  (Fe2O3.H2O)  is 
sometimes  found  as  crystals  which  were  originally  pyrite  (FeS2).  That 
is,  by  means  of  oxidation  and  hydration  pyrite  has  been  altered  to  limonite 
without  destroying  the  crystal  form.  Such  crystals  are  called  pseudo- 
morphs,  and  in  the  case,  just  referrred,  they  are  known  as  pseudomorphs 
of  limonite  after  pyrite.  There  are  several  interesting  types  of 
pseudomorphs. 

Paramorphs. — In  these  a  molecular  rearrangement  has  taken  place, 
without  the  chemical  composition  being  changed.  Paramorphs  are 
possible  only  in  the  case  of  polymorphous  substances.  Thus,  rutile 
(TiO2),  tetragonal,  after  brookite  (TiO2),  orthorhombic.  Also,  calcite 
(CaC03),  hexagonal,  after  aragonite  (CaCO3),  orthorhombic. 

Alteration  Pseudomorphs. — The  change  in  composition  may  involve 
the  loss  of  some  constituents,  the  addition  of  new  ones,  or  there  may 
be  a  partial  exchange.  Anhydrite  (CaSO4)  after  gypsum  (CaSO4.2H2O), 
malachite  (CuCO3.Cu(OH)2)  after  cuprite  (Cu2O),  and  kaolin  (H4Al2Si2O9) 


144  MINERALOGY 

after  orthoclase  (KAlSisOs)  are  excellent  illustrations  of  pseud omorphs  of 
this  type. 

Substitution  Pseudomorphs. — Sometimes  the  replacing  mineral  has  no 
chemical  relation  to  the  original  substance.  Good  illustrations  are  the 
pseudomorphs  of  quartz  (Si02)  after  fluorite  (CaF2),  and  quartz  after 
calcite  (CaCO3). 

Incrustation  Pseudomorphs. — At  times  a  mineral  may  be  deposited 
upon  the  crystal  form  of  another  and  completely  enclose  it.  Thus, 
smithsonite  (ZnCO3)  after  calcite  (CaC03)  (Fig.  520,  page  247).  In- 
crustation pseudomorphs  of  quartz  after  fluorite  are  sometimes  of  such 
a  character  as  to  permit  the  deposit  of  quartz  with  the  cubical  casts  of 
fluorite  to  be  removed  intact 


CHAPTER  XIII 
QUALITATIVE  BLOWPIPE  METHODS 

Whenever  possible  it  is  advisable  to  determine  minerals  at  sight, 
that  is,  by  means  of  their  physical  properties,  occurrences,  and  associates. 
It  frequently  becomes  necessary,  however,  to  supplement  these  observa- 
tions by  simple,  confirmatorj^  chemical  tests.  These  reactions,  obtained 
largely  at  high  temperatures  by  the  proper  use  of  the  blowpipe,  are 
referred  to  as  blowpipe  reactions.  The  chemist  in  his  laboratory  can  in- 
crease the  number  of  his  reagents  at  will  and  naturally  his  field  of  opera- 
tion is  larger  than  that  of  the  student  equipped 
with  a  blowpipe,  who  relies  upon  a  limited 
number  of  reagents  and  the  effects  produced 
when  minerals  are  subjected  to  the  oxidizing 
or  reducing  action  of  a  flame.  The  ease  with 
which  many  of  the  blowpipe  tests  are  obtained 
and  the  small  amount  of  apparatus  and  reagents 
required  have  made  these  reactions  popular  with 
both  the  mineralogist  and  geologist. 

The  equipment  which  is  necessary  may  be 
limited  to  the  following  apparatus  and  reagents. 

APPARATUS  FIG.    383.— George    J. 

Brush    (1831-1912).      For 
Blowpipe. — The  best  type  consists  of  a  brass       many  years   a  professor  in 

or  nickel  plated,  slightly  conical  shaped  tube  a  ^^^^J^ 
(Fig.  384)  about  18  cm.  in  length,  into  the  larger  of  Mowpipe  and  chemical 
end  of  which  fits  a  mouth  piece  of  hardened  S^^^L.detennilia" 
rubber  b.  At  the  opposite  end  a  hollow,  cylin- 
drical chamber  c,  serves  to  collect  the  moisture  which  condenses  in  the 
tube.  A  side  tube,  d,  joins  the  air  chamber  at  right  angles  and  is  equip- 
ped with  a  platinum  tip  e,  in  the  center  of  which  is  a  smooth  hole  from 
0.4  to  0.6  mm.  in  diameter. 

Lamps. — Where  illuminating  gas  is  available,  the  most  convenient 
form  of  lamp  is  the  Bunsen  burner  equipped  with  an  additional  inner 
tube  which  is  flattened  at  the  upper  end  and  cut  off  obliquely  (Fig. 
385).  The  supply  of  gas  should  be  so  regulated  that  a  luminous  flame 
about  4  cm.  in  height  results.  Where  gas  is  not  available  lamps  may 
be  secured  which  burn  either  liquid  (alcohol,  olive  oil,  lard  oil)  or  solid 
(tallow,  paraffin)  fuel.  By  the  addition  of  a  small  amount  of  turpentine 
10  145 


146  MINERALOGY 

to  the  alcohol  the  luminosity  as  well  as  the  reducing  power  of  the  flame  is 
greatly  increased.     A  candle  flame  may  also  be  used  to  advantage. 

Forceps. — Plain  iron,  or  better  still  platinum  tipped,  forceps  are  indis- 
pensable for  testing  the  fusibility  of  minerals  as  well  as  for  noting  flame 
colorations. 

Charcoal. — Rectangular  blocks  of  charcoal  about  10  X  2J^  X  2J^  cm. 
are  useful  supports  during  the  fusion  of  the  assay.  Likewise  films  are 
often  condensed  and  deposited  on  the  cooler  portion  of  the  support. 
Charcoal  made  from  willow,  pine,  or  basswood  is  usually  recommended. 
Plaster  Tablets. — These  are  made  by  preparing  a  thin  paste  of  plaster 
of  Paris  and  water,  and  spreading  it  over  an  oiled  glass  plate  until  a  uni- 
form thickness  of  about  5  mm.  is  secured.  Before  the  plaster  has  hard- 
ened the  surface  is  ruled  by  a  knife  into  rectangular  divisions  10  cm.  long 
and  about  5  cm.  wide.  These  tablets  are  especially  well 
adapted  for  the  condensation  of  iodide  sublimates. 

Platinum  Wire. — No  suitable  substitute  has  been  found 
to  replace  platinum  wire  for  flame  colorations  and  bead 
•   tests.     The  wire  should  be  No.  27  or  28 
B.  &  S.  gauge,  about  10  cm.  long.     One 
end  should  be  fused  into  a  piece  of  glass 
tubing. 

Hammer  and  Anvil. — A  small  hammer 
weighing  about  75  g.  with  a  wire  handle 
is  recommended.     Also  a  block  of  steel  4 
FIG.   384.—        FIG.  385.— Bun-  cm.  square  and  1  cm.  thick,  for  crushing 

Blowpipe.       sen  burner  with  in-   material  to  be  tested< 

HOP  "HlDGo 

Agate  Mortar  and  Pestle. — The  mortar 
should  be  at  least  4  cm.  in  diameter.  It  is  used  for  pulverizing  material. 

Diamond  Mortar. — The  mortar  should  be  of  tool-steel,  about  4  cm. 
square  and  possess  a  cylindrical  cavity  to  receive  the  pestle.  It  is  indis- 
pensable in  crushing  minerals  to  a  fairly  fine  powder. 

Open  and  Closed  Tubes. — Hard  glass  tubing,  12-14  cm.  in  length  and 
about  5  mm.  inside  diameter,  is  employed  either  open  at  both  ends  to 
note  the  effect  of  a  current  of  heated  air  upon  the  mineral,  or  closed  at 
one  end  for  the  detection  of  volatile  acids. 

Merwin  Flame-color  Screen. — This  is  a  celluloid  screen,  7%  X  12J^  cm., 
consisting  of  three  colored  strips,  one  blue,  one  violet,  and  one  blue  over 
violet.  The  strips  are  so  stained  as  to  absorb  the  orange  and  yellow 
portions  of  the  spectrum.  This  screen  is  extremely  useful  in  the  examina- 
tion of  flame  colorations  and  is  far  superior  to  the  "blue"  and  " green 
glass"  formerly  employed  for  the  same  purpose. 

Other  articles  for  blowpipe  work  which  need  no  detailed  description 
are  the  following: 

Test-tubes. — 12  cm.  in  length  and  15  mm.  in  diameter. 


QUALITATIVE  BLOWPIPE  METHODS 


147 


Test-tube  Stand,  Test-tube  Brush  and  Holder. 
Magnet. — Horseshoe  type. 
Watch-glasses. — 5  cm.  in  diameter. 

Glass  Funnel  and  Filter  Paper. — Bunsen  rapid  filtering  funnel  65  mm. 
in  diameter. 

File. — Triangular  for  cutting  glass  tubing. 

Pliers. — Serviceable  in  breaking  and  cutting  fragments  of  minerals. 

Figure  386  shows  an  assembly  of  the  above  apparatus. 


FIG.  386. — Assembly  of  apparatus  frequently  used  in  blowpipe  methods. 


DRY  REAGENTS 

These  reagents  should  be  kept  in  wide  mouthed  glass  bottles. 

Sodium  Carbonate,  Na2CO3;  or  Sodium  Bicarbonate,  NaHCO3.  Em- 
ployed extensively  in  the  decomposition  of  minerals. 

Borax,  Na2B4O7.10H2O.  When  fused  in  a  loop  of  platinum  wire  it 
is  used  for  bead  tests.  Borax  glass  is  fused  and  pulverized  borax. 

Microcosmic  Salt  or  Salt  of  Phosphorus,  HNaNH4PO4.4H2O.  Also 
used  for  bead  tests.  Upon  heating,  water  and  ammonia  are  liberated 
and  the  salt  is  transformed  to  sodium  metaphosphate,  NaPO3. 

Test-papers. — Blue  and  red  litmus  for  alkaline  and  acid  reactions. 
Yellow  turmeric  paper  for  the  detection  of  boracic  acid  and  zirconium. 

Potassium  Bisulphate,  KHSO4.  Used  in  fusions  for  decomposing 
minerals. 

Bismuth  Flux. — An  intimate  mixture  of  one  part  by  weight  of  KI, 


148  MINERALOGY 

one  part  of  KHS04,  and  two  parts  of  S.  When  used  on  the  plaster  sup- 
port many  elements  yield  highly  colored  iodide  sublimates. 

Boracic  Acid  Flux. — Consists  of  three  parts  of  finely  pulverized 
KHSO4  and  one  part  of  powdered  fluorite  (CaF2).  Employed  for  the 
detection  of  boron  in  silicates. 

Potassium  Nitrate,  KNO3.  When  used  with  a  fusion  mixture  it 
accelerates  oxidation. 

Granulated  Tin  and  Zinc. — Used  in  acid  solutions  to  affect  reduction. 

Magnesium  Ribbon. — For  the  detection  of  phosphoric  acid. 

LIQUID  REAGENTS 

Work  in  the  field  demands  that  the  number  of  reagents,  and  especially 
those  of  the  liquid  type,  be  reduced  to  a  minimum.  Under  these  condi- 
tions it  is  possible  to  restrict  the  number  of  wet  reagents  to  ammonia, 
a  10  per  cent,  solution  of  cobalt  nitrate,  and  the  common  acids,  HC1,HN03, 
and  H2SO4.  In  the  laboratory  it  is  far  better  to  augment  this  number  in 
order  to  materially  extend  the  range  of  operations. 

Alcohol. — 95  per  cent,  ethyl  alcohol. 

Ammonium  Hydroxide,  NH4OH.  One  part  of  the  concentrated 
alkali  diluted  with  two  parts  of  water. 

Ammonium  Molybdate,  (NH4)2Mo04.  Dissolve  50  g.  of  Mo03  in  a 
mixture  of  200  cc.  water  and  40  cc.  NH4OH  (sp.  gr.  0.90).  The  solution 
should  be  kept  warm.  The  liquid  is  then  filtered  and  poured  with  con- 
stant stirring  into  a  mixture  of  200  cc.  HN03  acid  (sp.  gr.  1.42)  and  300 
cc.  of  water. 

Ammonium  Oxalate,  (NH4)2C2O4.2H20.  20  g.  dissolved  in  500  cc. 
of  water. 

Barium  Chloride,  BaCl2.2H20.     30^  g.  dissolved  in  500  cc.  of  water. 

Calcium  Hydroxide,  (Lime  Water),  Ca(OH)2.  Prepared  by  shaking 
CaO  with  water  and  decanting  the  clear  liquid. 

Cobalt  Nitrate,  CO(NO3)2.6H2O.  One  part  of  the  crystallized  salt  is 
dissolved  in  10  parts  of  water  and  the  solution  kept  in  dropping  bottles. 

Dimethylglyoxime,  C4H8O2N2.  Prepare  a  saturated  solution  in  50  per 
cent,  alcohol  to  which  a  small  amount  of  ammonia  has  been  added. 

Di-sodium  Hydrogen  Phosphate  (Sodium  Phosphate),  Na2HP04. 
12H2O.  30  g.  dissolved  in  500  cc.  of  water. 

Ferrous  Sulphate,  FeSO4.7H2O.     Solution  prepared  as  needed. 

Hydrobromic  Acid,  HBr.  Prepared  by  passing  H2S  through  a  solu- 
tion of  bromine  in  water  until  the  red  color  of  the  liquid  bromine  dis- 
appears. The  flask  should  be  cooled  with  running  water  while  being 
charged. 

Hydrochloric  Acid,  HC1.  The  C.P.  concentrated  acid  is  diluted  with 
an  equal  volume  of  water. 


QUALITATIVE  BLOWPIPE  METHODS  149 

Hydrogen  Peroxide,  H2O2.     3  per  cent,  solution. 

Lead  Acetate,  Pb(C2H3O2)2.3H2O.  47>^  g-  dissolved  in  500  cc.  of 
water. 

Nitric  Acid,  HNO3.  Used  either  in  its  concentrated  form  or  one  part 
of  the  acid  is  diluted  with  two  parts  of  water. 

Nitrohydrochloric  Acid  (Aqua,  Regia).  A  mixture  of  3  parts  of  con- 
centrated HC1  acid  and  1  part  of  concentrated  HNO8  acid. 

Potassium  Ferricyanide,  K3Fe(CN)6.  27^  g.  dissolved  in  500  cc.  of 
water. 

Potassium  Ferrocyanide,  K4Fe(CN)6.3H2O.  26 J^  g.  dissolved  in 
500  cc.  of  water. 

Potassium  Hydroxide,  KOH.  The  " sticks"  should  be  kept  in  well 
stoppered  bottles  and  dissolved  in  water  when  needed. 


FIG.  387.—  The  Butler  blowpipe  set  suitable  for  field  use.  * 

Silver  Nitrate,  AgNO3.  21^  g.  dissolved  in  500  cc.  of  water.  The 
solution  should  be  kept  in  amber  colored  bottles. 

Sodium  Nitroferricyanide,  Na2Fe(NO)(CN)5.  Solution  should  be 
prepared  as  needed. 

Stannous  Chloride,  SnCl2.2H2O.     Solid  reagent. 

Sulphuric  Acid,  H2SO4.  Used  at  times  in  its  concentrated  form, 
also  diluted  with  four  parts  of  water.  In  diluting  the  acid  should  be 
added  very  slowly  to  the  water. 

Yellow  Ammonium  Sulphide,  (NH4)2SX.  Add  flowers  of  sulphur  to 
concentrated  ammonia  and  saturate  the  solution  with  H2S.  Dilute  with 
two  volumes  of  water.  The  flask  should  be  cooled  with  running  water 
while  being  charged  with  H2S. 

*  Arranged  by  Professor  G.  M.  Butler  and  sold  by  the  Denver  Fire  Clay  Company, 
Denver,  Colorado. 


150  MINERALOGY 

On  account  of  the  ease  with  which  blowpipe  reactions  may  be  obtained 
and  the  simplicity  of  the  equipment  necessary,  various  portable  sets 
suitable  for  field  work  have  been  arranged.  One  of  the  best  is  the 
Butler  Blowpipe  set,  illustrated  in  Fig.  387. 

STRUCTURE  AND  USE  OF  THE  FLAME 

Structure  of  the  Flame. — The  structure  of  the  flame  is  essentially 
the  same  whether  produced,  by  burning  a  gaseous,  liquid,  or  solid  fuel. 
If  a  small  luminous  flame  of  the  Bunsen  burner  be  examined  carefully, 
it  will  be  noted  that  four  more  or  less  distinct  zones  are  present  (Fig. 
388).  Immediately  above  the  burner  is  a  dark  cone,  a,  consisting 
primarily  of  unburned  gases.  Surrounding  the  dark  zone  and  extending 
beneath  the  luminous  mantle,  is  a  small,  blue,  non-luminous  zone,  6. 
The  strongly  luminous  region,  c,  which  emits  a  bright  yellow  light, 
constitutes  the  largest  portion  of  the  luminous  flame. 

In  general,  luminosity  may  be  due  to  three  causes 
operating  either  separately  or  jointly  in  increasing  the 
light  producing  property  of  a  flame.  These  causes  are 
(1)  the  temperature  of  the  flame,  (2)  the  density  of  the 
flame  gases,  and  (3)  the  presence  of  solid  particles  which 
are  heated  to  incandescence.  In  the  case  of  the  Bunsen 
burner  fed  with  ordinary  coal-gas  the  luminosity  is  un- 
FIQ  388  —  Questionably  due  to  the  presence  of  solid  particles  of 
Structure  of  lu-  carbon.  The  illuminants,  which  determine  the  light  giving 
mmous  flame.  prOperty  of  a  coal-gas  flame,  are  the  unsaturated  hydro- 
carbons, such  as  ethylene  C2H4,  acetylene  C2H2,  and  benzene  C6H6.  Due 
to  the  heat  of  combustion  these  hydrocarbons  undergo  dissociation. 
Ethylene  breaks  down  giving  acetylene  and  hydrogen,  while  the  acety- 
lene yields  carbon  and  hydrogen,  thus  explaining  the  cause  of  the  lumi- 
nosity. The  equations  expressing  this  dissociation  may  be  written  as 
follows : 

O2H4 — ^O2H2  -f~  H2 
C2H2-»2C  +  H2 

Finally  surrounding  the  luminous  mantle  we  have  an  outer,  non-luminous, 
invisible  zone,  d,  in  which  due  to  the  oxygen  of  the  air  there  is  almost 
complete  oxidation  yielding  as  end  products  CO2  and  H2O. 

The  Bunsen  flame  may  be  modified  by  inserting  an  inner  tube  which 
is  flattened  at  one  end  and  cut  off  obliquely,  so  that  the  blowpipe  flame 
can.be  directed  downward.  The  tube  also  acts  as  a  support  for  the 
blowpipe. 

Oxidizing  and  Reducing  Flames. — The  oxidizing  blowpipe  flame  is 
produced  by  inserting  the  tip  of  the  blowpipe  into  the  luminous  flame, 
which  should  be  about  4  cm.  in  height,  and  blowing  a  gentle  but 


QUALITATIVE  BLOWPIPE  METHODS  151 

steady  current  of  air.  The  flame  is  directed  slightly  downward  and 
immediately  becomes  non-luminous,  with  the  possible  exception  of 
a  very  small  luminous  region  above  the  blow  pipe  tip  Two  well- 
defined  non-luminous  zones  are  radily  produced,  a  and  6,  Fig.  389. 
The  non-luminosity  of  this  flame  may  be  explained  by  the  dilution  and 
cooling  effect  of  the  air  introduced  into  the  flame  gases,  thus  preventing 
the  dissociation  of  the  hydrocarbons  which  is  so  essential  for  the  pro- 
duction of  luminosity.  Not  only  does  the  flame  become  non- 
luminous  but  it  is  also  reduced  in  size.  Since  the  same  amount  of  gas  is 
consumed  and  the  ultimate  end  products  are  the  same  in  both  cases, 
the  heat  liberated  would  likewise  be  the  same  in  both  instances.  As 
the  non-luminous  flame  is  smaller  it  follows  that  the  average  tempera- 
ture of  this  flame  must  necessarily  be  higher  than  that  of  the  luminous 
flame.  The  zone  a  is  slightly  reducing  in  character  due  to  the  presence 
of  CO  in  this  region.  For  oxidation  purposes  the  substance  to  be  tested 
should  be  placed  as  indicated  by  the  position  of  the  loop  (Fig.  389). 
When  placed  in  this  position  the  highly  heated 
substance  readily  unites  with  the  oxygen  of  the 
atmosphere. 

The  oxidizing  blowpipe  flame  is  also  frequently 
employed  in  testing  the  fusibility  of  minerals.     The 
hottest  portion  of  this  flame  is  to  be  found  at  c.     FIG-  389.— Oxidizing 
In  testing  for  fusibility  the  fragment,  which  should 

extend  beyond  the  tip  of  the  forceps,  should  be  small,  possess  sharp  edges, 
and  be  held  in  the  hottest  portion  of  the  flame.  If  the  sharp  outlines 
are  rounded  the  mineral  is  said  to  be  fusible.  The  degree  of  fusibility  may 
be  roughly  determined  by  comparison  with  the  fusibility  of  minerals  com- 
prising a  standard  scale.  It  is  quite  important  that  fragments  should  be 
chosen  of  approximately  the  same  size.  The  generally  accepted  Scale  of 
Fusibility  is  composed  of  the  following  six  minerals  beginning  with  the 
most  fusible. 

Stibnite,  fuses  readily  in  a  candle  flame,  also  in  a  closed  tube. 

Chalcopyrite,  fuses  in  the  luminous  gas  flame,  but  with  difficulty 
in  a  closed  tube. 

Almandite  (Garnet),  fuses  readily  in  the  blowpipe  flame,  infusible 
in  the  luminous  gas  flame. 

Actinolite,  edges  are  readily  rounded  in  the  blowpipe  flame. 

Orthoclase,  edges  are  fused  with  difficulty  in  the  blowpipe  flame. 

Bronzite,  only  the  sharpest  splinters  are  rounded  by  fusion. 

The  reducing  blowpipe  flame  is  produced  by  placing  the  blowpipe  tip 
just  outside  of  the  flame  while  blowing  a  gentle  current  of  air  (Fig. 
390) .  The  flame  is  tilted  sideways  but  retains  its  luminosity.  A 
fragment  held  in  the  luminous  portion  of  this  flame  will  suffer  reduc- 
tion by  virtue  of  the  hot  carbon  particles  of  the  flame.  Thus  by 


152  MINERALOGY 

simply  shifting  the  position  of  the  blowpipe  and  regulating  the  strength 
of   the   blast,    entirely    opposite   chemical    effects   may  be   produced. 
The  purity  of  the  oxidizing  and  reducing  flames  may  be  readily  tested 
by  dissolving  a  few  small  particles  of  Mn(>2  in  a 
borax  bead  on  a  platinum  wire.     In  the  oxidizing 
flame  the  color  of  the  bead  should  be  reddish  violet, 
while    under  the  influence  of  the  reducing  flame 
FIG.  390. — Reducing     the  color  should  entirely  disappear. 

flame<  Scope  of  the  Chemical  Reactions.— The  reac- 

tions to  be  described  will  be  presented  in  the  following  order: 

1.  Reactions  on  plaster  tablet. 

(a)  Assay  heated  per  se. 

(b)  Assay  heated  with  reagents. 

2.  Reactions  on  charcoal  support. 

(a)  Assay  heated  per  se. 

(b)  Assay  heated  with  reagents. 

3.  Flame  colorations. 

4.  Bead  tests. 

5.  Heating  in  open  tube. 

6.  Heating  in  closed  tube. 

7.  Special  tests. 

8.  Summary  of  chemical  and  blowpipe  tests  for  the  more  important 
elements. 


1.   REACTIONS  ON  PLASTER  TABLET 

On  account  of  their  smooth  white  surface,  infusibility,  conductivity, 
and  porosity,  plaster  tablets  have  become  one  of  the  most  important 
supports  for  blowpipe  work.  They  can  be  employed  with  both  solid 
and  liquid  reagents.  The  tablets  are  cheaply  and  easily  made  and  their 
cleanliness  in  handling  has  added  to  their  popularity. 

Per  Se  Reactions. — A  small  depression  to  hold  the  assay  is  made 
in  the  lower  portion  of  the  tablet  and  the  support  held  in  an  inclined 
position.  Unless  otherwise  stated  the  oxidizing  blowpipe  flame  is  then 
directed  upon  the  assay.  The  volatile  constituent,  either  the  metal 
itself  or  an  oxide  of  the  metal,  is  driven  off  by  the  heat  and  deposited 
upon  the  cooler  portions  of  the  support.  The  more  important  per  se 
tests  are  given  on  page  153. 

While  some  characteristic  coatings  are  thus  obtained  by  merely 
heating  the  substance  per  se,  the  use  of  reagents  greatly  increases  the 
number  of  elements  which  can  be  easily  differentiated.  The  reagents 
usually  employed  on  the  plaster  support  are  bismuth  flux,  yellow  ammo- 
nium sulphide,  hydrobromic  acid,  and  cobalt  nitrate. 


QUALITATIVE  BLOWPIPE  METHODS 


153 


Indication 


Color  of  coating 


Remarks 


Cadmium 


Carbon 


Molybdenum 


Arsenic 
(metal) 


Arsenic 
(sulphide) 

Mercury 


Selenium 


Tellurium 


Silver 


Gold 


Near  assay,  reddish  brown  to 
greenish  yellow,  at  times  some- 
what iridescent.  At  a  distance 
brownish  black. 


Brownish 
coating. 


black,     non-volatile 


In  oxidizing  flame,  near  assay, 
yellowish  white,  crystalline  coat- 
ing of  MoO3. 


White  over  brownish  black,  very 
volatile  coating. 


Yellowish  to  reddish  browi) 
coating. 

Drab  gray,  extremely  volatile 
^sublimate. 

Cherry  red  to  crimson  in  thin 
layers.  Black  near  assay  where| 
coating  is  very  thick. 


Volatile  brown  to  black  coating, 
at  times  with  narrow  fringe  of 
blue  near  assay. 


Yellowish  coating  near  assay. 
When  touched  with  reducing 
flame,  becomes  brownish  and 
mottled. 

Slightly  purple  to  rose  colored 
coating  near  assay. 


Film  is  due  to  an  oxide,  is  per- 
manent, and  is  best  obtained  from 
metallic  cadmium. 


Obtained  from  carbonaceous  ma- 
terial, such  as  asphalt. 

When  touched  with  reducing 
flame,  white  coating  is  imme- 
diately changed  to  deep  blue. 
Example,  ammonium  molybdate. 


Garlic  odor  is  also  noted,  due 
probably  to  small  amount  .  of 
arsine. 

When  heated  too  rapidly,  coating 
becomes  brownish  black. 

Example,  HgS  or  HgO. 


Sublimate  is  due  to  metal,  is 
volatile,  and  yields  reddish  fumes 
with  odor  of  rotten  horse-radish. 
Example,  metallic  selenium. 

A  drop  of  cone.  H2SO4  added  to 
brown  coating  and  gently  heated 
yields  effervescent  pink  of  tellu- 
rium sulphate.  Example,  metal- 
lic tellurium. 

Coating  is  permanent  and  re- 
quires high  heat.  Reducedmetal 
may  also  be  noted.  Example, 
AgN03. 

Requires  very  intense  heat  and 
is  best  seen  when  tablet  is  cold. 


Reactions   with   Bismuth   Flux   and   Yellow  Ammonium   Sulphide. 

One  part  of  the  powdered  mineral  is  intimately  mixed  with  three  parts 
of  bismuth  flux  (consisting  of  two  parts  S,  one  part  Kl,  and  one  part 
KHSO4)  and  heated  on  a  plaster  support.  In  nearly  every  instance 
highly  colored,  volatile  iodide  coatings  are  obtained  which  condense 


154 


MINERALOGY 


on  the  cooler  parts  of  the  tablet.  Similarly  colored  sublimates  can  be 
easily  differentiated  by  the  use  of  yellow  ammonium  sulphide,  which 
transforms  the  iodide  films  to  sulphides.  The  accompanying  table 
summarizes  the  most  satisfactory  iodide  reactions. 


Indication 


Color  of  coating 


.Remarks 


Arsenic 


Antimony 


Lead 


Thallium 


Bismuth 


Mercury 


Silver 


Selenium 


Tellurium 


Lemon  to  orange  yellow  coating. 
Coating  disappears  when  sub- 
jected to  ammonia  fumes. 

Orange  to  peach  red  sublimate. 
Disappears  when  subjected  to 
ammonia  fumes. 


Chrome  yellow  coating. 


Orange  yellow  film  near  assay, 
with  purplish-black  band  at  dist- 
ance. Entire  coating  ultimately 
changes  to  yellow. 

Chocolate  brown  with  underly- 
ing crimson.  Yellowish  on  outer 
margins. 


Combination  of  scarlet,  yellow, 
and  greenish-black. 

Slight    yellowish    coating    near 
assay. 


Reddish  brown  to  scarlet. 


Purplish  brown  to  black  coating. 


A  drop  of  (NHOoSz  on  coating 
yields  yellow  ring.  Single  drop  of 
NH4OH  dissolves  ring  completely. 

A  drop  of  (NH4)2Sa;  on  coating 
produces  orange  red  ring,  which  is 
not  dissolved  by  single  drop  of 
NH4OH. 

(NH4)2SX  applied  to  film  yields 
black  spot,  often  surrounded  by 
reddish  cloud. 

(NH4)2SZ  applied  to  yellow  coat- 
ing gives  chocolate  brown  spot. 


When  subjected  to  ammonia 
fumes  brown  coating  changes  to 
orange  yellow  and  then  to  cherry 
red. 

If  strongly  heated  predominating 
color  is  yellowish-green. 

Requires  intense  heat.  When 
touched  with  reducing  flame  be- 
comes pinkish  brown  and  some- 
what mottled. 


Reddish  fumes  given  off. 
is  colored  indigo  blue. 


Flame 


A  drop  of  cone.  H2SO4  added  to 
coating  and  gently  heated  yields 
an  effervescent  pink. 


Combination  of  Elements. — On  account  of  the  difference  in  degree  of 
volatility  of  the  iodides,  it  is  not  difficult  at  times  to  determine  more  than 
one  element,  capable  of  giving  iodide  coatings,  at  a  single  operation. 


QUALITATIVE  BLOWPIPE  METHODS 


155 


Thus,  in  the  case  of  jamesonite,  Pb2Sb2S5,  when  the  powder  is  heated  with 
bismuth  flux,  the  peach  red  antimony  iodide  coating  is  the  first  to  appear 
at  a  distance  from  the  assay.  As  the  temperature  is  increased  the  less 
volatile  chrome  yellow  coating  of  lead  iodide  forms  near  the  assay.  The 
use  of  yellow  ammonium  sulphide  can  also  be  used  to  advantage  to  detect 
such  a  combination.  Near  the  assay  a  black  spot  with  a  reddish  cloud 
indicates  the  presence  of  lead,  while  at  a  distance  a  well  defined  red 
antimony  ring  is  obtained.  Iodides  of  the  same  or  nearly  the  same  degree 
of  volatility  are  deposited  together  producing  a  compound  coating  with 
a  resultant  color  which  may  serve  to  indicate  the  individual  components. 
Reactions  with  Hydrobromic  Acid. — The  porosity  of  the  plaster 
tablet  lends  itself  readily  to  the  application  of  the  liquid  reagent  hydro- 
bromic  acid.  To  the  assay,  placed  in  a  slight  depression  as  heretofore, 
is  slowly  added  6  to  8  drops  of  the  acid.  The  liquid  is  quickly  absorbed 
by  the  support  and  returned  as  needed  to  the  assay  when  the  latter  is 
heated  with  the  blowpipe  flame.  Hydrobromic  acid  can  be  prepared  by 
passing  H2S  through  a  mixture  of  bromine  in  water  until  the  red  color  of 
the  liquid  bromine  disappears.  The  elements  not  previously  recorded, 
which  yield  bromide  reactions,  are  copper  and  iron. 


Indication 

Color  of  coating 

Uemarks 

Copper 
Iron 

Volatile,  purplish  coating,  mot- 
tled with  black. 

Rust  colored  spots. 

On  standing  frequently  changes 
to  yellow.     Flame  is  colored  green. 

Non-volatile  and  deposited  near 
assay. 

As  the  copper  bromide  is  more  volatile  than  that  of  the  iron  it  is 
possible  to  detect  both  in  a  single  operation.  By  applying  the  blowpipe 
flame  to  the  space  immediately  surrounding  the  assay,  the  copper  coating 
can  easily  be  driven  to  the  upper  portions  of  the  tablet  thus  revealing 
the  rust  colored  spots  of  iron  near  the  assay.  In  addition  to  the  copper 
and  iron  reactions,  molybdenum,  bismuth,  lead,  and  mercury  may  also 
produce  the  following  colored  films  with  HBr. 

Molybdenum — volatile,  blue  to  bluish  green  coating. 

Bismuth — volatile,  yellow  or  crimson  sublimate. 

Lead — canary  yellow  film. 

Mercury — volatile  yellow  coating. 

Cobalt  Nitrate  Reactions. — Crystallized  cobalt  nitrate  is  dissolved 
in  10  parts  of  water  and  kept  in  convenient  dropping  bottles.  The  appli- 
cation of  this  reagent  is  restricted  to  white  or  light  colored,  infusible 
minerals.  Fusible  compounds  would  invariably  yield  blue  cobalt  glasses. 


156 


MINERALOGY 


The  pulverized  mineral  is  placed  on  a  plaster  tablet  and  strongly  ignited 
with  the  oxidizing  flame,  a  drop  or  two  of  cobalt  nitrate  is  then  added 
and  the  assay  intensely  heated  a  second  time.  Upon  cooling  the  assay 
may  be  seen  to  have  assumed  a  definite  color  due  to  combination  with 
the  cobalt  oxide.  If  the  mineral  is  sufficiently  porous  to  absorb  the 
cobalt  nitrate,  the  liquid  can  be  applied  directly  to  the  fragment  without 
previous  pulverization.  The  cobalt  nitrate  reactions  are  especially 
serviceable  in  the  detection  of  magnesium,  aluminium,  zinc,  and  tin. 


Indication 


Color 


Remarks 


MgO  and  minerals  con- 
taining it. 

A12O3  and  compounds 
containing  it.  Zinc 
silicates. 

ZnO  and  minerals  con- 
taining it. 


Pink  or  pale  flesh  red. 


Blue. 


Bright  green. 


Bluish  green. 


Best  seen  when  cold.     Example, 
brucite. 

Examples,     kaolinite,     hemimor- 
phite. 


Can  be  applied  to  fragment  or 
to  white  coating  on  charcoal 
Example,  smithsonite. 

Should  be  applied  to  white  coat- 
ing on  charcoal. 


2.  REACTIONS  ON  CHARCOAL  SUPPORT 

When  plaster  tablets  are  not  available  or  when  it  is  desirable  to  verify 
the  presence  of  an  element,  recourse  may  be  had  to  the  charcoal  support, 
for  the  reactions  obtained  on  plaster  and  charcoal  supplement  each  other. 
Plaster  is  the  better  conductor  and  the  sublimates  formed  are  found  nearer 
the  assay.  Charcoal,  on  the  other  hand,  aids  the  reducing  flame  when- 
ever reduction  is  desired.  Care  must  be  exercised  not  to  mistake  the 
ash  of  the  charcoal  for  a  sublimate.  The  ash  will  form  near  the  assay 
where  the  heat  has  been  intense  and  will  not  obscure  the  grain  of  the 
charcoal,  sublimates  on  the  other  hand  have  a  tendency  to  conceal  the 
grain. 

Per  Se  Reactions. — A  small  depression  is  made  near  the  edge  of 
the  charcoal  and  the  assay  is  heated  slowly  with  the  oxidizing  flame, 
while  the  support  is  held  in  an  inclined  position  to  catch  the  subli- 
mate formed.  If  the  assay  decrepitates  (snaps)  when  heated  it  should 
be  finely  pulverized  and  moistened  with  a  drop  of  water.  The  films 
produced  when  heat  is  applied  slowly  are  mainly  oxides  as  is  shown  by 
the  accompanying  table. 


QUALITATIVE  BLOWPIPE  METHODS 


157 


Indication 


Color  and  character  of  sublimate 


Remarks 


Arsenic 
Antimony 

Cadmium 
Molybdenum 

Lead 

Bismuth 

Zinc 

Tin 

Selenium 

Tellurium 
Thallium 


White  (As2O3),  very  volatile 
coating. 

Near  assay,  dense  white  coating 
(Sb2O3,  Sb2O4).  At  distance, 
bluish. 

Near  assay — black  to  reddish 
brown  (GdO).  At  distance,  yel- 
lowish-green. 

Pale  yellow  (MoO3),  hot;  white, 
cold;  crystalline. 


Dark   yellow    (PbO)    hot;   pale 
yellow,  cold. 

Orange  yellow  (Bi2O3),  hot;  lemon 
yellow,  cold. 

Canary  yellow  (ZnO),  hot;  white, 
cold. 

Faint  yellow  (SnO2),  hot;  white, 
cold. 

Near    assay,    steel    gray     with 
metallic      luster.     At      distance, 
white  (SeO)  2  tinged  with  red  (Se). 

Near  assay,    white  (TeO2).      At 
distance,  gray  (Te)  or  brownish. 

White  (T12O),  very  volatile. 


Deposits  at  distance  from  assay. 
Garlic  odor  often  noted. 

Less  volatile  than  arsenic  coating. 


Very  thin  deposits  show  irides- 
cent tarnish. 


When  touched  with  reducing 
flame  becomes  dark  blue.  Copper 
red  (MoO2)  coating  surrounding 
assay. 

At  times  mixed  with  white  sul- 
phite and  sulphate  of  lead. 

Distinguished  from  lead  by  bis- 
muth flux  test. 

When  moistened  with  Co(NO3)2 
and  heated,  becomes  grass  green. 

When  moistened  with  Co(XO3)2 
and  heated,  becomes  bluish  green. 

Coating  colors  the  flame  blue. 
Characteristic  odor. 


Imparts  pale  green  color  to  flame. 


Coating  colors  flame  bright  green. 


In  addition  to  the  above,  white  sublimates  may  result  from  the  volatil- 
ization of  the  chlorides  of  copper,  lead,  mercury,  ammonium,  and  the 
alkalies. 

While  the  charcoal  support  does  not  lend  itself  readily  to  the  use  of 
liquids,  solid  reagents  such  as  bismuth  flux  and  sodium  carbonate  are 
frequently  employed. 

Reactions  with  Bismuth  Flux. — The  reactions  of  the  elements  with 
bismuth  flux  on  charcoal  are,  on  the  whole,  rather  unsatisfactory  with  the 
following  two  exceptions: 

Lead — greenish  yellow  film. 

Bismuth — yellowish  white  sublimate  with  crimson  border. 


158  MINERALOGY 

Reactions  with  Sodium  Carbonate. — The  effect  of  heating  the  assay 
with  Na2CO3  on  charcoal  is  to  augment  the  reducing  action  of  the  hot 
charcoal.  This  is  due  to  the  formation  of  reducing  gases,  such  as  CO, 
and  possibly  gaseous  sodium.  Under  this  treatment  a  number  of  sub- 
stances are  reduced  to.  the  metallic  condition.  The  assay  is  mixed  with 
three  parts  of  anhydrous  Na2CO3  together  with  some  powdered  charcoal 
obtained  from  the  pit  made  to  support  the  assay.  After  heating  with  the 
reducing  flame  for  several  minutes  the  fusion  is  ground  with  water  in 
an  agate  mortar  and  the  color,  malleability,  or  magnetism  of  the  reduced 
particles  noted.  In  addition  to  reduced  metal,  some  substances  yield 
a  sublimate,  while  still  others  are  volatilized  so  quickly  that  no  reduced 
metal  is  formed. 

Summary  of  Na2CO8  Reactions. — The  reactions  of  the  common  ele- 
ments fall  under  three  divisions. 

1.  Reduced  metal  without  sublimate, 
(a)  Malleable  buttons — Cu,  Ag,  Au. 

Copper — confirm  by  dissolving  in  HN03  acid  and  note  blue  color 
when  solution  is  made  alkaline  with  NH4OH. 

Silver — dissolve  in  HN03  acid  and  note  white  precipitate  when  a  drop 
of  HC1  acid  is  added.  The  precipitate  is  soluble  in  NH4OH. 

Gold — confirm  by  dissolving  in  aqua  regia,  evaporate  almost  to 
dryness,  and  dissolve,  the  residue  in  a  little  water.  Add  a  few  drops  of 
freshly  prepared  SnCl2.  Finely  divided  precipitate  is  formed  which  ren- 
ders the  solution  purple  by  transmitted  light  and  brownish  by  reflected 
light. 

(fc)  Magnetic  particles — Fe304,  Co,  Ni. 

Iron — dissolve  in  HN03  acid,  add  a  few  drops  of  potassium  ferrocy- 
anide.  Dark  blue  precipitate  will  be  formed. 

Cobalt — dissolve  in  borax  bead  on  end  of  platinum  wire.  Note  blue 
color. 

Nickel — dissolve  in  HNO3  acid,  make  alkaline  with  NH4OH.  Add 
several  cc.  of  alcoholic  solution  of  dimethylglyoxime.  Bright  red  preci- 
pitate is  produced. 

2.  Reduced  Metal  with  Sublimate. 

Antimony — dense  white  coating  near  assay.     Gray  brittle  button. 
Lead — sulphur  yellow  coating.     Gray  malleable  button. 
Bismuth — lemon  yellow  sublimate.     Reddish  white,  brittle  button. 
Tin — white  coating  near  assay,  yellow  while  hot.     White  malleable 
button. 

3.  Sublimate   without    Metal. 

Arsenic — white  volatile  film.     Garlic  odor. 
Zinc — white  film,  yellow  while  hot. 

Cadmium — reddish  brown  to  orange  colored  sublimate  with  tarnish 
colors. 


QUALITATIVE  BLOWPIPE  METHODS  159 

Selenium — steel  gray  coating  and  brown  fumes  with  characteristic 
odor. 

Tellurium — white  coating  with  reddish  or  dark  yellow  border. 

Molybdenum — white  coating,  changed  to  dark  blue  when  exposed  to 
the  reducing  flame. 

Sodium  carbonate  can  also  be  profitably  employed  in  the  detection 
of  sulphur,  manganese,  chromium,  and  phosphorus. 

Test  for  Sulphur. — The  powdered  sulphide,  mixed  with  3  to  4  parts 
of  anhydrous  Na2CO3,  is  thoroughly  fused  on  a  charcoal  support.  In 
case  of  sulphates  some  powdered  charcoal  should  be  added  to  the  Na2C03. 
After  fusion  the  mass  (Na2S)  is  removed  from  the  support  and  crushed. 
One-half  of  the  powder  is  then  placed  upon  a  clean  silver  coin  and  several 
drops  of  water  are  added.  A  dark  brown  or  black  stain  (Ag2S)  indicates 
sulphur,  provided  selenium  and  tellurium  are  absent.  To  check  this 
sulphur  test  the  remaining  powder  is  placed  on  a  watch  glass.  Several 
drops  of  water  are  then  added,  followed  by  a  drop  or  two  of  freshly  pre- 
pared sodium  nitroferricyanide,  Na2Fe(NO)(CN)5.  An  intense  red 
purple  coloration  is  indicative  of  sulphur.  It  is  preferable  to  use  an 
alcohol  flame  for  the  fusion,  as  the  gas  flame  may  contain  sulphur  com- 
pounds. Also  there  is  a  tendency  for  the  fusion  to  sink  into  the  charcoal 
and  for  this  reason  the  same  pit  should  be  used  but  once. 

Tests  for  Manganese  and  Chromium. — Powdered  manganese  com- 
pounds should  be  mixed  with  a  small  amount  of  KNO3  and  placed  in  a 
shallow  depression  made  in  a  charcoal  support.  Sodium  carbonate  is 
then  spread  over  this  mixture.  The  blowpipe  flame  is  directed  for  a  brief 
period  on  a  given  spot  until  incipient  fusion  takes  place.  Upon  cooling 
this  fused  area  assumes  a  bluish-green  color  due  to  the  formation  of 
sodium  manganate,  Na2MnO4.  Long  fusion  is  to  be  avoided  as  the  man- 
ganate  loses  its  color,  due  to  reduction  brought  about  by  the  charcoal. 
(Copper  compounds  also  yield  bluish  green  fusions.) 

Chromium  compounds  when  fused  with  Na2CO3  and  KNO3  in  a  man- 
ner similar  to  that  indicated  for  manganese,  yield  yellow  colored  fusions 
(Na2CrO4) .  This  test  for  chromium  is,  however,  unsatisfactory  in  the 
presence  of  lead  or  vanadium  as  these  elements  also  yield  yellow  masses. 
Instead  of  performing  the  fusion  on  charcoal,  manganese  or  chromium 
compounds  may  be  dissolved  in  a  Na2CO3  bead  held  in  a  loop  of 
platinum  wire.  Under  the  influence  of  the  oxidizing  flame  of  the  blow- 
pipe the  bead  will  assume  the  color  indicated  above.  If  the  platinum 
wire  test  is  used,  it  is  not  necessary  to  add  KNO3  to  the  Na2CO3. 

Test  for  Phosphorus. — Phosphates  of  aluminium  and  the  heavy 
metals  should  be  fused  with  two  parts  of  Na2CO3  on  charcoal,  and  the 
powdered  fusion  then  ignited  in  a  test  tube  with  magnesium  ribbon. 
The  phosphorus  is  thereby  converted  into  a  phosphide  (Mg3P2),  which 
upon  the  addition  of  a  few  drops  of  water  liberates  the  unpleasant, 


160  MINERALOGY 

garlic-like  odor  of  phosphine,  PH3,  which  produces  a  black  coloration 
when  brought  in  contact  with  filter  paper  moistened  with  AgNO3. 
Phosphates  of  the  alkalies  and  alkaline  earths  may  be  ignited  with 
magnesium  ribbon  directly  without  previous  fusion.  This  test  for  phos- 
phorus cannot  be  relied  upon  in  the  presence  of  arsenic  or  antimony. 

A  more  reliable  test  for  phosphorus  is  the  following:  the  phosphate 
is  dissolved  in  HNO3  acid  (if  insoluble,  fusion  with  Na2CO3  should  precede 
solution  in  acid)  and  a  portion  of  the  filtrate  added  to  an  excess  of  ammo- 
nium molybdate  solution.  Upon  standing  or  upon  slightly  warming,  a 
yellow  precipitate  of  ammonium  phosphomolybdate  will  be  formed. 

3.    FLAME  COLORATIONS 

A  number  of  compounds  and  especially  those  of  the  alkalies  and  alka- 
line earths,  impart  to  the  non-luminous  flame  of  the  Bunsen  burner  or  to 
the  oxidizing  flame  of  the  blowpipe,  characteristic  colors  which  may  be 
used  for  their  identification.  As  the  intensity  of  the  flame  coloration 
depends  upon  the  volatility  of  the  salt  used,  and  inasmuch  as  chlorides 
are  generally  more  volatile  than  other  compounds,  the  best  results  are 
ordinarily  obtained  by  moistening  the  powder  with  HC1.  In  a  few 
instances  moistening  with  H2S04  is  preferable.  The  powder  is  intro- 
duced into  the  Bunsen  flame  by  means  of  a  clean  platinum  wire,  or  a 
very  thin  splintery  fragment  of  the  mineral,  moistened  with  acid,  may  be 
held  by  the  forceps  in  the  non-luminous  portion  of  the  oxidizing  blowpipe 
flame.  Fusible  metals  and  arsenic  should  not,  however,  be  heated  in  con- 
tact with  platinum  tipped  forceps.  To  detect  alkalies  in  silicates,  de- 
composition may  be  brought  about  by  mixing  the  assay  with  an  equal 
volume  of  powdered  gypsum  before  introducing  into  the  hottest  portion 
of  the  Bunsen  flame.  It  is  even  possible  at  times  to  detect  the  individual 
components  when  several  flame  coloring  elements  occur  together.  This 
may  be  accomplished  by  making  use  of  either  (1)  spectroscope,  or  (2) 
the  difference  in  degree  of  volatility  of  the  constituents  present,  or  (3) 
colored  screens. 

Spectroscope. — For  blowpipe  work  the  direct  vision  pocket  spectro- 
scope is  very  useful.  The  best  instruments  are  provided  with  a  scale  and 
a  comparison  prism  by  means  of  which  the  spectrum  of  an  unknown 
substance  can  be  directly  compared  with  that  of  a  known  substance. 
When  a  colored  flame  is  observed  through  a  spectroscope,  light  colored 
lines  are  perceived  upon  a  dark  back  ground.  The  color,  position,  and 
grouping  of  the  lines  are  used  as  the  basis  for  the  recognition  of  the 
elements. 

Difference  in  Volatility. — In  a  mixture  the  flame  coloring  consti- 
tuents can  often  be  detected  readily  without  the  use  of  the  spectroscope, 
by  noting  the  difference  in  the  degree  of  volatility  of  the  components.  In 
general  the  alkalies  (Na,  K,  Li)  are  more  volatile  than  the  alkaline 


QUALITATIVE  BLOWPIPE  METHODS 


161 


earths  (Ca,  Ba,  Sr),  and  by  holding  the  platinum  wire  about  1  mm. 
from  the  outer  non-luminous  Bunsen  flame  sufficient  heat  is  encountered 
to  volatilize  the  alkalies,  while  insertion  in  the  hotter  portion  of  the 
flame  is  necessary  to  detect  the  alkaline  earths. 

Colored  Screens. — These  are  also  extensively  employed  in  analyzing 
flame  mixtures.  Screens  composed  of  colored  glass  or  celluloid  transmit 
certain  rays  while  others  are  entirely  absorbed.  Thus,  blue  glass  absorbs 
certain  red  and  green  rays  together  with  those  of  yellow.  One  of  the 
most  effective  screens  on  the  market  at  present  is  the  Merwin  Flame 
Color  Screen.  This  celluloid  screen  is  composed  of  three  colored  strips, 
one  blue,  one  violet,  and  one  blue  over  violet.  The  strips  are  stained  so 
as  to  absorb  the  orange  and  yellow  portions  of  the  spectrum.  Observa- 
tions should  be  made  through  all  three  divisions  of  the  screen.  In  the 
accompanying  table  flame  colorations  will  be  recorded  as  seen  with  and 
without  the  Merwin  color  screen. 


Indication 

Flame  color 

Through  Merwin 
screen 

Remarks 

Calcium 

Yellowish- 

1.  Flash  of  green- 

Color  flashes  out  at  the  moment 

red 

ish-yellow1 

salt  becomes  incandescent.     Cal- 

2. Invisible 

cium   minerals  becomes   alkaline 

3.  Flash  of  crim- 

upon ignition. 

son 

Strontium 

Crimson 

1.  Invisible 

Strontium  minerals  become  alka- 

2. Invisible 

line  upon  ignition.     If  to  solution 

3.  Crimson 

of  Sr  salt  few  drops  of  BaCl2  are 

added,  red  color  (Sr)  will  appear 

after   green    of    Ba.    Sr   solutions 

yield  white  ppt.  when  few  drops  of 

H2SO4     are     added.     (Difference 

from  Li.) 

Lithium 

Carmine 

1.  Invisible 

Lithium  minerals  do  not  become 

2.  Invisible 

alkaline  upon  ignition.     If  to  solu- 

3. Crimson 

tion  of  Li  salt  few  drops  of  Bad* 

are    added,    red    color    (Li)   will 

appear  before  green  of  Ba. 

Potassium 

Pale  violet 

1.  Blue  violet 

Purplish  red  through  blue  glass. 

2.  Deep  red  violet 

Spectroscope  is  necessary  to  dis- 

3. Red  violet 

tinguish  between  potassium,    ru- 

bidium, and  caesium. 

Sodium 

Intense 

1.  Invisible 

Flame   color  should  be  intense 

yellow 

2.  Invisible 

and  persistent  to  indicate  sodium 

3.  Invisible 

mineral.     Invisible  through  blue 

glass. 

1  Numerals  refer  to  the  divisions  of  the  screen. 
II 


162 


MINERALOGY 


Indication 

Flame  color 

Through  Merwin 
screen 

Remarks 

Copper  oxide      1 

Emerald 

Tinged    with    azure    blue    when 

Copper  iodide    / 

green 

moistened  with  HC1. 

Thallium 

Grass  green 

Tellurium      \ 

Pale  green 

Antimony     / 

Phosphorous 

Pale  bluish 

1.  Green 

Should  be  moistened  with  con. 

green 

2.  Invisible 

H2SO4.     Color  not  very  distinct. 

3.  Red  violet 

Boron 

Yellowish 

1.  Bright  green 

For     borates     decomposed     by 

green 

2.  Faint  green 

H2SO4:  To  mineral  placed  in  por- 

3. Faint  green 

celain  dish,  add  alcohol  and  con- 

centrated   H2SO4,    apply   match. 

Note  yellowish  green  color  of  flame. 

For  borates  not   decomposed  by 

H2SO4:  Mix  powder  with  3  parts  of 

boracic  acid  flux  (3  parts  KHSO4, 

1  part  CaF2),  introduce  into  flame 

by  means  of  hot  Pt.  wire.     Flash 

of  green  will  be  seen  due  to  BF3. 

Barium 

Yellowish 

1.  Bright  green 

Barium  minerals  become  alkaline 

green 

2.  Faint  green 

upon  ignition. 

3.  Faint  green 

Molybdenum 

Faint    yel- 

If in  form  of  oxide  or  sulphide. 

lowish 

green 

Zinc 

Bluish 

Appears    as    bright    streaks    in 

green 

flame. 

Copper  chloride 

Azure  blue 

1.  Bright  green 

Flame    is    tinged    with    emerald 

2.  Bluish  green 

green. 

3.  Bluish  green 

Selenium 

Indigo  blue 

Accompanied     by     characteristic 

odor. 

Arsenic 

Livid  blue 

Lead 

Pale  azure 

Tinged  with  green  in  outer  parts. 

blue 

Indium 

Corn  flower 

blue 

QUALITATIVE  BLOWPIPE  METHODS 


163 


4.  BEAD  TESTS 

The  oxides  of  many  of  the  metals  form  complex  compounds  of  char- 
acteristic colors  when  dissolved  at  a  high  temperature  in  borax, 
Na2B4O7.10H2O,  or  microcosmic  salt  (salt  of  phosphorus)  HNaNH^O^- 
4H2O.  The  support  usually  employed  for  this  work  is  a  No.  28  B.  & 
S.  gauge  platinum  wire  about  10  cm.  long  which  has  been  fused  into  the 
end  of  a  piece  of  glass  tubing.  Unoxidized  metals  as  well  as  compounds 
sulphur,  arsenic,  and  antimony  should  be  roasted  until  the  volatile 
constituents  have  been  removed  and  the  residue  converted  into  an  oxide. 


Oxide  of 

Borax  bead 

Microscopic  salt  bead 

Oxidizing  flame 

Reducing  flame 

Oxidizing  flame 

Reducing  flame 

Mn 

reddish  violet 

colorless 

violet 

colorless 

Co 

blue 

blue 

blue 

blue 

Cu 

blue 

opaque  red 

blue 

opaque  red 

Ni 

reddish  brown 

opaque  gray 

straw  to  reddish 
yellow 

yellow  to  reddish 
yellow 

Fe 

yellow 

pale  green 

colorless    to   yel- 
lowish brown 

colorless  to  pale 
violet 

U 

yellow 

pale  green  to  color- 
less 

yellowish   green 

bright  green 

Cr 

grass  green 

emerald  green 

emerald  green 

emerald  green 

V 

yellowish  green 

emerald  green 

light  yellow 

emerald  green 

Ti 

colorless 

brownish  violet 

colorless 

violet 

Mo 

colorless 

brown 

colorless 

pure  green 

W 

colorless 

yellow  to  yellowish 
brown 

colorless 

fine  blue 

Si 

insoluble  skeleton 

insoluble  skeleton 

A  small  circular  loop  made  at  the  end  of  the  platinum  wire  is  heated 
and  then  touched  to  the  borax  or  microcosmic  salt.  Sufficient  material 
will  adhere  to  form,  when  heated  before  the  blowpipe  flame,  a  clear 
colorless  glass.  In  the  case  of  the  microcosmic  salt  bead  the  heat  should 
be  applied  slowly  as  the  material  has  a  tendency  to  drop  from  the  wire 
due  to  the  escape  of  water  and  ammonia.  By  touching  the  hot  bead  to  a 


164  MINERALOGY 

few  particles  of  the  finely  crushed  oxide,  and  again  heating  in  the  oxidiz- 
ing flame  of  the  blowpipe,  solution  and  coloration  of  the  fusion  will 
frequently  result.  The  color  of  the  bead  should  be  noted  after  it  has  been 
subjected  to  the  oxidizing  flame  and  again  after  the  reducing  flame  has 
been  applied.  The  action  of  the  reducing  flame  may  be  greatly  ac- 
celerated by  dissolving  a  small  fragment  of  SnO  or  SnCl2  in  the  bead. 
The  colors  observed  with  the  microcosmic  salt  are  not  in  every  instance 
identical  with  those  of  the  borax.  In  general  the  tests  obtained  with 
the  borax  flux  are  more  delicate,  while  the  microcosmic  salt  fusions  yield 
a  greater  variety  of  colors.  The  removal  of  the  bead  from  the  support 
for  preservation  may  be  accomplished  by  simply  straightening  the  wire. 
In  the  table  on  page  163,  the  colors  listed  are  those  of  the  cold  beads 
obtained  from  the  unmixed  oxides. 

Of  the  beads  enumerated,  the  first  eight  are  extremely  service- 
able. In  order  to  detect  Ni  in  the  presence  of  Co  or  any  other  oxide 
which  ordinarily  would  obscure  the  nickel  test,  the  procedure  should 
be  as  follows:  dissolve  several  beads  in  HNO3  acid  and  add  NH4OH 
until  the  solution  becomes  alkaline.  To  the  filtrate  add  several  cc.  of  an 
alcoholic  solution  of  dimethylglyoxime.  A  scarlet  precipitate  indicates 
Ni.  This  is  an  extremely  delicate  and  characteristic  test. 

Ni(NO3)2  +  2NH4OH  +   2C4H8N2O2    =    (C8H14N4O4)  Ni  +  2NH4N03 

+  2H2O. 
5.  OPEN  TUBE  REACTIONS 

Hard  glass  tubing,  15  to  20  cm.  long  and  about  5  mm.  in  diameter, 
is  employed  in  blowpipe  work  to  note  the  effects  of  a  current  of  air  when 
permitted    to   pass  over  a  highly  heated  substance. 
These  open  tubes  should  be  bent  slightly  near  one 
end  in  order  to  hold  the  material  more  conveniently 
which  should  be  in  a  powdered  condition  to  expose 
the  maximum  amount  of  surface.     The  tube  is  held  in 
an  inclined  position  in  the  flame,  apply  heat  first  above 
the  assay  to  insure  a  good  current  of  air  through 
the  tube,  and  then  directly  under  the  mineral  (Fig. 
FIG.  39  L— Heating    391).     In  most  instances  oxidation  results  and  the 
volatile  material  either  escapes  in  the  form  of  a  gas 
with   a    characteristic  odor,  or  a  sublimate  is  formed  which  deposits 
upon  the  cooler  portions  of  the  tube.     The  temperature  should  be  in- 
creased gradually  so  as  not  to  volatilize  the  substance  in  an  unoxidized 
condition.     The  results   of   open  tube   tests   may   be    summarized    as 
follows: 

A.  Gases  with  Characteristic  Odors 

1.  Odor  of  burning  sulphur  with  bleaching  properties.  The  gas 
liberated  is  SO2.  The  test  is  very  delicate  and  is  extremely  useful  in 


QUALITATIVE  BLOWPIPE  METHODS 


165 


testing  for  sulphur  or  sulphides.  If  oxidation  is  not  complete,  due  to  too 
rapid  heating  or  an  insufficient  air  supply,  free  sulphur  may  also  deposit 
on  the  sides  of  the  tube. 

2.  Garlic    odor.     Produced    when    arsenic    compounds    are  rapidly 
heated  and  not  completely  oxidized. 

3.  Odor  of  rotten  horseradish.     Obtained  from  selenium  compounds 
when  volatilized. 

B.  Sublimates 


Indication 


Character  of  the  coating 


Remarks 


Arsenic 
Arsenides 
Sulphides  of 
arsenic 

Antimony 
Sulphides  of 
antimony 


Bismuth 
sulphide 

Bismuth  (free 
from  sulphur) 

Tellurium 
Tellurides 

Lead  chloride 


Lead  sulphide 


Selenium 
Selenides 


Molybdenum 
oxide  or  sul- 
phide 

Mercury 

Amalgams 


White,  crystalline,  and  volatile 
sublimate  (As2Os).  Crystals  are 
minute  octahedrons. 


Dense  white  fumes  which  partly 
escape  and  partly  condense  as 
white  powder.  Both  Sb2Os  and 
Sb2O4  are  formed. 

White,  non-volatile  powder  (Bi 


Brown  while  hot;  yellow  when 
cold  (Bi2O3). 

Snow  white,  non-volatile  subli- 
mate (TeO2). 

White,  partially  volatile  subli- 
mate (PbOCl). 

Non-volatile,  white  powder 
formed  near  assay  (PbSOO. 

Near  assay,  steel  gray,  volatile 
coating  consisting  of  radiating 
needles  (SeO2). 

Yellow  when  hot,  white  when 
cold  (MoOs). 


Minute,  gray,  metallic  globules. 
Volatile  (Hg). 


Metallic  mirror  or  yellow  coating 
of  arsenic  sulphide  indicates  too 
rapid  heating. 


Sb2Os  is  white,  slowly  volatile, 
and  crystalline.  Sb2C>4  is  non- 
volatile and  amorphous. 


Fusible  to  yellow  drop. 


Sublimate  is  fusible. 


Upon  heating  fuses  to  colorless 
drops. 

Fusible  to  yellow  drops. 


Fusible  to  yellow  drops,   white 
when  cold. 

At  distance  reddish  due  to  finely 
divided  Se. 


Collects  ne?r  assay  as  mass  of 
delicate  crystals. 


Globules  unite  by  rubbing  with 
strip  of  paper. 


6.  CLOSED  TUBE  REACTIONS 

Closed  tube  reactions  are  carried  out  in  hard  glass  tubes  about  four 
inches  long  and  6  mm.  in  diameter,  which  are  closed  at  one  end.     The 


166  MINERALOGY 

assay  is  introduced  in  the  form  of  small  fragments  and  heat  applied 
gradually.  The  object  of  this  treatment  is  to  note  the  effect  of  heat 
without  oxidation  as  the  air  is  practically  entirely  excluded  (Fig.  392). 
These  are  known  as  the  per  se  tests.  Closed  tubes  may  also  be 
profitably  employed  in  heating  the  assay  with  KHSC>4. 

A.  Per  Se  Tests 

The  applicaton  of  heat  alone  may  produce  such  phenomena  as: 

(a)  Change  in  appearance  or  character  of  assay. 

1.  Change  in  Color. — The  more  important  minerals  thus  affected  are: 
Copper  minerals — blue  or  green,  become  black  when  hot;  black,  cold. 
Zinc  minerals — white  or  colorless,  become  pale  yellow  when  hot; 
white,  cold. 

Manganese   and    cobalt   minerals — pink,   become   black   when   hot; 
black,  cold. 

Lead  and  bismuth  minerals — white  or  colorless,  be- 
come dark  yellow  to  brown  when  hot;  pale  yellow  to 
white,  cold. 

Iron  minerals — green  or  brown,  become  black  when 
hot;  black,  cold. 

Hematite — dark  red,  becomes  black  when  hot;  dark 
red,  cold. 

FIG.  392.—         2.  Fusion. — Only  minerals  with  a  fusibility  below  one 
Heating  in  closed  anc[  one-half  in  the  scale  of  fusibility  melt  when  heated  in 

tube. 

a  closed  tube  per  se. 

3.  Carbonization. — Indicating  organic  substances. 

4.  Phosphorescence. — Some  minerals  when  heated   to  a  temperature 
below  redness  and  viewed  in  a  dark  room  will  be  seen  to  emit  colored 
light.     Many  varieties  of  fluorite  when  heated  to  150°  C.  emit  a  purple 
or  green  light. 

5.  Decrepitation. — Alkaline    chlorides,   galena,    and    many  minerals 
snap  and  break  down  to  a  fine  powder  when  heated.     This  behavior  is 
usually  the  result  of  unequal  expansion  or  due  to  the  presence  of  water 
held  mechanically. 

6.  Magnetization. — Iron  minerals  frequently  become  magnetic  upon 
the  application  of  heat. 

(b)  Formation  of  Gases  in  the  Tube. 

1.  Carbon  Dioxide. — Colorless  and   odorless  gas.     A   drop   of  lime 
water   held   in   a   loop   of   platinum   wire   becomes  turbid.     Indicates 
carbonates. 

2.  Oxygen. — A  glowing  splinter  takes  fire  when  held  in  the  tube. 
Indicates  peroxides,  nitrates,  chlorates,  bromates,  or  iodates. 

3.  Ammonia. — Characteristic    odor    and    alkaline    reaction.     More 
pronounced  when  heated  with  Na2CO8.     Indicates  ammonium  salts  or 


QUALITATIVE  BLOWPIPE  METHODS 


167 


organic  compounds  containing  nitrogen.     If  the  latter,  the  mass  usually 
chars. 

(c)  Formation  of  Sublimates. 

1.  'Colorless  or  White  Sublimates 


Indication 


Character  of  sublimate 


Remarks 


Water 


Ammonium 
salts 

Lead   chloride 

Mercurous 
chloride 

Mercuric 
chloride 

Antimony 
oxide 

Arsenic  oxide 


Tellurium 
oxide 


Colorless,  volatile  liquid  which 
forms  on  the  cooler  part  of  the 
tube. 

White,  very  volatile. 

White,  fusing  to  yellow  drops. 
White,  yellow  when  hot. 

White,  yellow  when  hot. 
White,  fusible. 
White,  volatile. 

Pale  yellow,  hot;  colorless  to 
white  globules,  cold. 


Indicates  water  of  crystallization 
or  hydroxyl.  Neutral  if  pure, 
may  show  acid  or  alkaline 
reaction. 


Sublimate  is  infusible. 
Sublimate  is  fusible. 

Sublimate  consists  of  needle  like 
crystals. 

Sublimate  consists  of  octahedral 
crystals. 

Obtained  from  tellurium  and  a 
few  of  its  compounds. 


2.  Colored  Sublimates 


Indication 


Character  of  sublimate 


Remarks 


Sulphur 
Some  sulphides 

Sulphides  of 
arsenic 

Sulphides  of 
antimony 

Sulphide  of 
mercury 

Selenium 
Selenides 

Arsenic 
Arsenides 

Mercury 
Amalgam 

Tellurium 
Tellurides 


Brownish  red  liquid,  hot;  pale 
yellow  crystalline  solid,  cold. 

Dark   red   liquid,    hot;   reddish 
yellow  solid,  cold. 

Black  when  hot;  reddish  brown 
when  cold.     Sb2OS2  is  formed. 

Brilliant  black  solid. 

Black     fusible     globules.     Red 
when  rubbed. 

Brilliant  black  sublimate.     Gray 
and  crystalline  near  heated  end. 

Minute,  gray  metallic  globules. 
Black  fusible  globules. 


Due  to  the  formation  of  free 
sulphur. 

From  realgar,  orpiment  and  sul- 
pharsenites. 

From  sulphides  and  sulphanti- 
monites. 

Yields  a  red  powder  when 
rubbed. 

Sublimate   forms   only   at   high 
temperature. 

Garlic  odor  noted  when  tube  is 
broken  below  mirror  and  gently 
heated. 

Globules  unite  when  nibbed. 

Sublimate  forms  at  high  tem- 
perature. 


168 


MINERALOGY 


B.  Reactions  in  Closed  Tube  with  KHSO4 


The  detection  of  volatile  acids  may  be  accomplished  by  gently  heat- 
ing the  assay  with  an  equal  volume  of  KHSO4". 

1.  Colored  Gas  Evolved 


Indication 

Character  of  gas 

R  emarks 

Nitrates 

Reddish    brown    with    pungent 

Gas  liberated  is  NO2. 

Nitrites 

odor. 

Chlorates 

Yellowish  green  fumes  with  odor 

Gas  liberated  is  C1O2. 

of  chlorine. 

Iodides 

Violet  vapors  accompanied  by  a 

Iodine  is  set  free. 

black  metallic  sublimate. 

Bromides 

Heavy  brownish  red  vapor  with 

Bromine  is  liberated.     Best  seen 

Bro  mates 

pungent  odor. 

when  tube  is  held  against  a  white 

back  ground. 

2.  Colorless,  Odorous  Gas  Evolved 

Indication 

Character  of  sublimate 

Remarks 

Sulphates 

Suffocating  odor  with  bleaching 

Gas  is  SO2. 

Sulphites 

properties. 

Chlorides 

Colorless      gas      which      fumes 

Gas  is  HC1. 

strongly   when   in    contact   with 

NH4OH. 

Fluorides 

Gas  which  etches  the  tube  above 

Gas  is  HF. 

the  assay. 

Sulphides 

Gas  with  odor  of  decayed  eggs. 

Gas  is  H2S. 

Blackens  lead  acetate  paper. 

Acetates 

Gas  with  odor  of  vinegar. 

Gas  is  C2H4O2. 

3.  Colorless,  Odorless  Gas  Evolved 

Indication 

Character  of  sublimate 

Remarks 

Carbonates 

A  drop  of  lime  water  held  in  a 

Gas  is  CO2. 

loop   of  platinum   wire  becomes 

turbid. 

Oxalates 

A  gas  which  burns  with  a  blue 

Gas  is  CO. 

flame. 

QUALITATIVE  BLOWPIPE  METHODS  169 

7.  SPECIAL  TESTS 

In  this  section  reactions  will  be  listed  which  do  not  conveniently 
fall  under  any  of  the  previous  divisions.  They  are  nevertheless  extremely 
useful  in  mineralogical  determinations.  The  reactions  given  below  are 
to  be  considered  as  individual  tests  and  not  in  any  way  related  to  one 
another. 

1.  Tests  for  Calcite  and  Aragonite. — Powdered  calcite  when  boiled 
for  a  few  minutes  in  a  dilute  solution  of  cobalt  nitrate  remains  white  or  in 
the  presence  of  organic  matter  becomes  yellowish,  while  aragonite  turns 
lilac  red  due  to  the  formation  of  a  basic  cobalt  carbonate.     This  is 
commonly  known  as  Meigen's  test.     The  change  in  color  is  more  readily 
detected  by  washing  the  powder  by  decantation  after  boiling.     Inasmuch 
as  barium  or  strontium  carbonate  and  precipitated  basic  magnesium 
carbonate  give  the  same  reactions  as  aragonite,  and  dolomite  the  same  as 
calcite.  it  is  absolutely  necessary  to  first  establish  the  fact  that  you  are 
dealing  with  one  of  the  modifications  of  CaC03  before  applying  the  cobalt 
nitrate  test. 

2.  Tests  for  Calcite  and  Dolomite. — (a)  Calcite  dissolves  in  acetic 
acid  with  a  brisk  evolution  of  C02,  while  dolomite  is  not  appreciably 
affected  by  the  cold  acid. 

(6)  J.  Lemberg  has  noted  that  powdered  calcite  is  colored  violet  when 
treated  with  a  solution  of  aluminium  chloride  and  extract  of  logwood, 
while  dolomite  remains  unchanged.  The  reaction  is  caused  by  the 
precipitation  upon  the  calcite  of  A1(OH)3  which  absorbs  the  dye  and 
acts  as  a  mordant.  To  observe  the  color  change  the  powder  should  be 
washed  by  decantation.  The  Lemberg  solution  is  prepared  by  boiling 
for  twenty  minutes  a  mixture  of  4  grams  of  A1C13,  6  grams  extract  of  log- 
wood, and  60  grams  of  water,  with  constant  stirring  and  with  the  addi- 
tion of  the  amount  of  water  lost  by  evaporation. 

(c)  According  to  F.  Cornu  calcite  and  dolomite  may  be  distinguished 
by  covering  the  powder  with  a  small  amount  of  water  and  adding  a  few 
drops  of  phenolphtalein  solution.  Upon  shaking,  the  aqueous  solution 
above  the  calcite  assumes  a  pink  to  red  color  while  the  dolomite  is  not 
appreciably  affected. 

3.  Test  for  Cassiterite  (SnO2). — As  the  usual  colors  of  cassiterite  are 
various  shades  of  yellow,  brown,  or  black  a  change  in  the  appearance  of 
the  mineral  can  be  utilized  for  its  detection.     This  can  readily  be  accom- 
plished by  placing  fragments  of  cassiterite  in  contact  with  metallic  zinc 
and  adding  dilute  HC1  acid.     The  nascent  hydrogen  liberated  reduces  the 
SnO2  and  the  mineral  becomes  coated  in  a  few  minutes  with  a  thin  gray 
layer  of  metallic  tin. 

4.  Reduction  Tests  with  Metallic  Tin  and  HC1  Acid.— Rapid  tests 
for  the  elements  titanium,  tungsten,  niobium  and,  vanadium  may  be 


170 


MINERALOGY 


carried  out  by  dissolving  the  Na2CO3  fusion  in  HC1  and  adding  a 
few  fragments  of  metallic  tin.  The  hydrogen  evolved  reduces  the  salts 
of  the  rarer  elements  producing  colored  solutions  or  precipitates  which 
are  used  to  detect  the  presence  of  the  element  involved.  The  following 
table  indicates  the  changes  referred  to. 


Indication 


Color  of  solution 


Remarks 


Titanium 
Tungsten 

Niobium 
Vanadium 


Violet  color. 


Dark  blue. 


Pale  blue. 


Blue,  green,  finally  blue  violet. 


Best  seen  when  evolution  of  H2 
ceases. 

Color  due  to  heavy  precipitate 
which  upon  standing  settles  to 
bottom. 

Color  disappears  upon  addition 
of  water. 

Metallic  zinc  should  be  used  in- 
stead of  tin. 


Instead  of  using  a  reducing  agent  for  the  detection  of  titanium  and 
vanadium,  H2O2  in  an  acid  solution  can  be  employed.  The  oxidation 
reactions  are  more  delicate  than  the  corresponding  reduction  tests. 


Titanium 


Vanadium 


Amber  colored  solution. 


Reddish  brown  solution. 


The  fused  mass  should  be  dis- 
solved in  1  : 1  H2SO4  solution. 

Dissolve  fusion  in  HNO3. 


8.  SUMMARY    OF  CHEMICAL   AND    BLOWPIPE    TESTS   FOR   THE  MORE 
IMPORTANT  ELEMENTS 

For  convenience  of  reference  the  most  reliable  tests  for  the  various 
elements  are  here  summarized.  The  wet  chemical  tests  included  in  this 
summary  are  often  extremely  useful  and  supplement  the  dry  reactions. 


ALUMINUM  (Al) 

(1)  Ignition  with  Cobalt  Nitrate. — Infusible  light  colored  aluminum 
minerals  when  moistened  with  a  drop  or  two  of  cobalt  nitrate  and  in- 
tensely  ignited    assume    a   blue  color.     (Zinc   silicates   give  a  similar 
reaction.) 

(2)  Precipitation  with  Ammonia. — When  an  acid  solution  containing 
aluminum  is  rendered  alkaline  with  NH4OH,  a  white  gelatinous  precipi- 


QUALITATIVE  BLOWPIPE  METHODS  171 

tate  of  Al(OH)  3  is  formed.     This  precipitate  is  readily  dissolved  in  a  warm 
KOH  solution. 

AMMONIUM  (NH4) 

(1)  Heating  in  Closed  Tube. — When  boiled  with  a  solution  of  KOH,  or 
heated  with  Na2CO3  or  CaO,  ammonia  is  evolved  which  is  recognized  by 
its  odor,  alkaline  reaction,  and  white  fumes  when  brought  in  contact 
with  HC1. 

ANTIMONY  (Sb) 

(1)  Sublimate   on  Plaster   Tablet. — Antimony  minerals   mixed   with 
bismuth  flux  and  heated  on  a  plaster  support  yield  an  orange  to  peach 
red  sublimate.    A  drop  of  (NH  4)283:  upon  the  coating  produces  an  orange 
red  ring. 

(2)  Sublimate  on  Charcoal. — When  heated  with  the  oxidizing  flame 
on  charcoal  a  dense  white  sublimate  of  Sb2O3  is  formed  near  the  assay. 
The  coating  is  volatile  and  bluish  in  thin  layers.     The  fumes  have  no 
distinctive  odor  (difference  from  arsenic). 

(3)  Heating  in  Open  Tube. — Antimony  minerals   yield  dense  white 
fumes  which  partly  escape  and  partly  condense  as  a  white  powder. 

(4)  Heating  with  Concentrated  Nitric  Acid.— HNO3  oxidizes  antimony 
and  its  sulphides  to  metantimonic  acid  which  is  a   white  precipitate, 
insoluble  in  both  water  and  HNO3. 


ARSENIC  (As) 

(1)  Sublimate  on  Plaster  Tablet. — Arsenic  minerals  mixed    with  bis- 
muth flux  and  heated  on  a  plaster  support  yield  a  lemon  yellow  sublimate. 
A  drop  of  (NH4)2Ss  on  the  coating  produces  a  yellow  ring. 

(2)  Sublimate    on   Charcoal. — Arsenic,    arsenides,    and    sulphides    of 
arsenic  heated  with  the  oxidizing  flame  on  charcoal  give  a  very  volatile 
white  coating  of As2O3  which  deposits  at  some  distance  from  the  assay. 
The  fumes  have  a  characteristic  garlic  odor. 

(3)  Heating  in  Open  Tube. — Arsenic,  arsenides,  and  sulphides  produce 
a  white,  volatile,  and  crystalline  sublimate  of  As2O3.    Too  rapid  heating 
may  yield  a  metallic  mirror  instead  of  the  oxide. 

(4)  Heating  in  Closed  Tube. — Arsenic  and  arsenides  give  a   bright 
metallic  mirror.    When  the  tube  is  broken  below  the  mirror  and  heated, 
a  garlic  odor  will  be  noted.    Arsenates  should  be  mixed  with  powdered 
charcoal  to  cause  reduction. 

(5)  Precipitation   as   Ammonium   Magnesium    Ar senate. — With    few 
exceptions  arsenic  minerals  are  oxidized  when  boiled  with  concentrated 
HNO3  to  arsenic  acid,  H->AsO4.    Make  the  solution  alkaline  with  NH4OH 
and  filter.     To  the  filtrate  add  a  few  cc.  of  magnesia  mixture  (MgCl2 


172  MINERALOGY 

and   NH4C1),    shake   and    let   stand.    White    crystalline   MgNH4As04 
will  precipitate. 

BARIUM  (Ba) 

(1)  Flame  Test. — When  moistened  with  HC1  barium  minerals  impart 
a  yellowish  green  color  to  the  flame. 

(2)  Alkaline  Reaction  and  High  Specific  Gravity: — Barium  compounds 
are  characterized  by  rather  high  specific  gravities  and  alkaline  reaction 
with  moistened  turmeric  paper  after  strong  ignition. 

(3)  Precipitation  as  Barium  Sulphate. — A  few  drops  of  dilute  H2SO4 
will  precipitate  white  BaS04,  insoluble  in  dilute  acids.     This  test  dis- 
tinguishes barium  from  boron  and  phosphorus  minerals  which  also  color 
the  flame  green. 

BERYLLIUM  (Be);  ALSO  CALLED  GLUCINUM 

Beryllium    compounds    resemble   very   closely   aluminum    in   their 
chemical  reactions.     A  few  distinguishing  tests  are: 

(1)  Precipitation  as  Basic  Carbonate. — Ammonium  carbonate  added 
to  a  solution  of  a  beryllium  salt  produces  a  white  precipitate  of  beryllium 
carbonate,  readily  soluble  in  an  excess  of  the  reagent  (difference  from 
Al).     Upon  boiling  the  solution  beryllium  is  precipitated  as  white  basic 
carbonate. 

(2)  Solution  of  Hydroxide  in  Acid  Sodium  Carbonate. — A  saturated 
solution  of  NaHCO3  upon  the  hydroxides  of  iron,  aluminum,  and  beryl- 
lium, dissolves  the  beryllium  hydroxide.     If  the  mineral  is  a  silicate, 
fusion  with  Na2C03  on  charcoal,  and  evaporation  to  dryness  with  HC1 
for  the  removal  of  silica  must  precede  the  foregoing  tests. 

BISMUTH  (Bi). 

(1)  Sublimate  on  Plaster  Tablet. — When  mixed  with  bismuth  flux  and 
heated  on  a  plaster  support  bismuth  minerals  yield  a  chocolate  brown 
coating,  which  is  changed  to  a  bright  red  when  exposed  to  strong  ammonia 
fumes. 

(2)  Bismuth  Flux  on  Charcoal. — Upon  charcoal  the  mineral  mixed  with 
bismuth  flux  produces  a  yellowish  sublimate  with  crimson  border. 

(3)  Reduction  on  Charcoal. — Bismuth  compounds  mixed  with  Na2CO3 
on  charcoal  give  a  lemon  yellow  coating  with  white  border,  and  reddish 
white  brittle  buttons. 

(4)  Precipitation  as  Bismuth  Oxychloride.' — If  water  is  added  to  an 
HC1  solution,  which  has  been  evaporated  almost  to  dryness,  a  white 
precipitate  of  BiOCl  is  formed. 


QUALITA TIVE  BLOWPIPE  METHODS  *  173 

BORON  (B) 

(1)  Flame  Test. — Some  boron  minerals  yield  a  yellowish  green  flame 
when  heated  alone,  but  the  majority  require  the  application  of  H2SO4 
or  boracic  acid  flux.  If  decomposable  by  H2SO4,  boron  compounds 
burn  with  a  yellowish  green  flame  due  to  the  formation  of  basic  acid 
methyl  ester,  B(OCH3)3,  when  placed  in  an  evaporating  dish  with  alcohol 
and  concentrated  H2SO4  and  ignited.  Borates  not  decomposable  by 
H2SO4  should  be  mixed  with  three  parts  of  boracic  acid  flux  (three 
parts  KHSO4,  one  part  CaF2)  and  introduced  into  the  flame  on  a  clean 
platinum  wire.  A  flash  of  green  indicates  the  liberation  of  the  volatile 
boron  fluoride  BF3. 

(2)  Turmeric  Paper  Test. — If  turmeric  paper  is  moistened  with  a  dilute 
HC1  solution  of  boron  and  dried  it  assumes  a  reddish  brown  color.  If  it 
is  then  moistened  with  NH4OH  a  bluish  black  or  grayish  blue  spot  results, 
depending  upon  the  amount  of  turmeric  and  boric  acid  present.  It  is 
advisable  to  run  a  blank  test  at  the  same  time.  As  acid  solutions  of 
zirconic,  titanic,  tantalic,  niobic,  and  molybdic  acids  also  color  turmeric 
paper  brown,  this  test  for  boron  can  only  be  employed  in  their  absence. 

BROMINE  (Br) 

(1)  Heating  in   Closed   Tube  with  Potassium    Bisulphate. — -When    a 
bromide  is  heated  with  KHS04,  heavy  brownish  red  vapors  of  bromine  are 
liberated. 

(2)  Precipitation  as  Silver  Bromide. — A  white  precipitate  of  AgBr 
(soluble  in  NH4OH)  is  formed  when  AgNO3  is  added  to  a  dilute  HNO3 
solution  of  a  bromide. 

CADMIUM  (Cd) 

(1)  Heating  on  Plaster  Tablet  Per  Se. — Near  the  assay  there  is  formed 
a  reddish  brown  to  greenish  yellow  coating.     At  a  distance  it  is  brownish 
black.    It  is  best  obtained  from  the  metal. 

(2)  Heating  on  Charcoal. — -When  heated  on  charcoal  cadmium  yields 
a  film  which  is  reddish  brown  near  the  assay  and  yellowish  green  at  a 
distance.    Very  thin  deposits  show  an  iridescent  tarnish. 

CALCIUM  (Ca) 

(1)  Flame  Test. — After  being  pulverized  and  moistened  with  HC1 
many  calcium  minerals  color  the  non-luminous  flame  yellowish  red. 
The  color  should  not  be  confused  with  the  redder  and  more  persistent 
strontium  flame.  When  viewed  through  the  Merwin  Color  Screen, 
calcium  appears  as  a  flash  of  greenish  yellow  through  division  No.  1. 
(Distinction  from  Li  and  Sr.) 


174  MINERALOGY 

(2)  Precipitation  as  Calcium  Oxalate. — Ammonium  oxalate  added  to 
an  ammoniacal  solution  of  calcium  produces  a  white  precipitate  of  cal- 
cium oxalate,  CaC204.    This  precipitate  will  also  form  in  a  very  slightly 
acid  solution. 

(3)  Precipitation  as  Calcium  Sulphate. — A  few  drops  of  dilute  H2S04 
added  to  a  calcium  salt  dissolved  in  a  small  volume  of  dilute  HC1  pre- 
cipitates CaSO4.    Upon  the  addition  of  water  and  the  application  of  heat 
the  precipitate  dissolves.    (Distinction  from  barium  and  strontium.) 

CARBON  (C) 

(1)  Heating   in   Closed  Tube. — -When  heated,  hydrocarbons  such  as 
asphaltum,  albertite,  or  bituminous  coals  yield  oils  and  tarry  compounds 
which  condense  on  the  sides  of  the  tube.    The  residue,  if  any,  is  mainly 
carbon.    If  carbon  is  present  as  carbonates,  decomposition  is  affected 
with  the  liberation  of  C02  which  renders  a  drop  of  lime  water  on  a  loop 
of  Pt  wire  turbid. 

(2)  Effervescence  with  Acids. — The  solution  of  carbonates  in  dilute 
acids  takes  place  with  brisk  evolution  of  CO2.    In  some  instances  the  acid 
should  be  heated  but  care  must  be  exercised  not  to  mistake  boiling  for 
liberation  of  C02. 

CERIUM  (Ce) 

Oxidation  with  Hydrogen  Peroxide. — If  a  cerous  salt  is  treated  with  a 
slight  excess  of  NH4OH'  and  then  with  H2O2,  the  white  precipitate  be- 
comes reddish  orange  in  color,  due  probably  to  Ce(OH)  3O2H.  To  remove 
interfering  elements  precede  as  follows:  Fuse  with  Na2CO3  and  evapo- 
rate the  HC1  solution  to  dryness.  Take  up  with  dilute  HC1  and  filter. 
Precipitate  the  cerous  oxalate  from  the  dilute  acid  solution  by  means  of 
ammonium  oxalate.  Filter  and  dissolve  the  precipitate  in  warm  concen- 
trated HC1.  Make  ammoniacal  with  NH4OH  and  white  Ce(OH)3  is 
formed.  Upon  oxidation  with  H202  its  color  is  changed  to  reddish  orange. 

CHLORINE  (Cl) 

(1)  Flame  Coloration  with  Copper  Oxide. — If  a  hot  salt  of  phosphorus 
bead  saturated  with  CuO  is  brought  in  contact  with  a  chloride  and  then 
heated  in  the  non-luminous  flame,  copper  chloride  will  be  formed  which 
will  tinge  the  flame  azure  blue.     (Bromine  gives  a  similar  reaction.) 

(2)  Liberation  of  Chlorine. — If  a  chloride  is  mixed  with  KHSO4  and  a 
small  amount  of  MnO2  and  then  heated  in  a  closed  tube,  free  chlorine  is 
set  free.     AgCl  and  silicates  containing   chlorine  require  fusion   with 
Na2C03. 

(3)  Precipitation  as  Silver  Chloride. — A  few  drops  of  AgNO3  added 
to  a  chloride  in  a  dilute  HNO3  solution  precipitates  white  curdy  AgCl, 


9 

QUALITA TIVE  BLOWPIPE  METHODS  175 

soluble    in    NH4OH.     This    is    an    extremely    delicate    test.    Minerals 
insoluble  in  HNO3  should  be  fused  with  Na2CO3. 

CHROMIUM  (Cr) 

(1)  Bead  Tests. — Chromium  colors  borax  and  microcosmic  salt  beads 
an  emerald  green,  in  both  the  oxidizing  and  reducing  flames. 

(2)  Fusion  with  Sodium  Carbonate  on  Platinum  Wire. — When   chro- 
mium compounds  are  dissolved  in  a  Na2CO3  bead  under  the  influence  of 
the  oxidizing  flame,  the  fusion  is  colored  a  light  yellow      If  instead  of 
Pt  wire,  a  charcoal  support  is  used,  a  little  KNO3  should  be  added  to  the 
Na2CO3  to  offset  the  reducing  action  of  the  support. 

(3)  Precipitation  as  Lead  Chromate. — Fuse  with  Na2CO3  and  KNO3 
on  charcoal.    Leach  with  water,  make  slightly  acid  with  acetic  acid,  and 
add  a  few  drops  of  lead  acetate.    A  yellow  precipitate  of  lead  chromave 
will  be  formed. 

(4)  Oxidation  to  Per  chromic  A  dd.—  Dissolve  the  fusion  in  water  and 
acidify  with  dilute  H2SO4.    To  the  cold  solution  add  H2O2  and  a  blue 
color  of  H3CrO8  is  obtained.    Perchromic  acid  is  very  unstable  and  the 
color  may  last  but  a  few  seconds. 

COBALT  (Co) 

(1)  Bead  Tests. — Cobalt  imparts  a  blue  color  to  the  borax  and  salt  of 
phosphorus  beads,  in  both  the  oxidizing  and  reducing  flames.  When 
copper  and  nickel  interfere,  fuse  the  bead  on  charcoal  with  a  particle 
of  metallic  tin.  Cu  and  Ni  are  reduced  to  the  metallic  condition  and  the 
blue  color  of  cobalt  will  appear. 

COLUMBITJM  (Cb).    SEE  NIOBIUM 

COPPER  (Cu) 

(1)  Sublimate  on  Plaster   Tablet. — When  moistened  with    HBr  and 
heated  on  a  plaster  support  copper  minerals  yield  a  volatile  purplish 
coating,  mottled  with  black. 

(2)  Flame  Test. — Oxides  of  copper  color  the  flame  emerald   green, 
while  moistening  with  HC1  produces  an  intense  azure  blue. 

(3)  Bead  Tests. — Under  the  influence  of  the  oxidizing   flame  borax 
and  microcosmic  salt  beads  are  green  when  hot,  and  blue  when  cold.    In 
the  reducing  flame  Cu2O  is  formed  which  colors  the  beads  on  opaque  red. 

(4)  Reduction  to  Metal  on  Charcoal. — When  heated  on  charcoal  with  a 
mixture  of  Na2CO3  and  borax,  copper  minerals  yield  globules  of  metallic 
copper.     Sulphides  should  first  be  roasted  before  reducing. 


176  MINERALOGY 

(5)  Blue   Solution  with  Ammonium  Hydroxide. — A  copper  solution 
made  alkaline  with  NH4OH  assumes  a  deep  blue  color. 

FLUORINE  (F) 

(1)  Etching  Glass  Tube.— When  mixed  with  four  or  five  parts  of  KHSO4 
or  with  sodium  metaphosphate  (obtained  by  fusing  salt  of  phosphorus) 
and  then  heated  in  a  closed  tube  many  powdered  fluorides  liberate  HF, 
which  etches  the  glass  near  the  assay.    In  addition  a  ring  of  SiO^may  form 
in  the  upper  part  of  the  tube.    The  etching  of  the  glass  may  be  seen  to 
best  advantage  by  breaking  the  closed  end  of  the  tube,  washing  out  its 
contents  and  drying  the  tube  over  a  flame  when  the  glass  will  appear 
clouded  near  the  assay. 

(2)  Flame  Test. — Fluorides  mixed  with  KHS04  and  borax  and  intro- 
duced into  the  Bunsen  flame  on  a  platinum  wire  give  a  flash  of  green  due 
to  the  volatilization  of  BF8. 

GLUCINUM  (G);  SEE  BERYLLIUM 
GOLD  (Au) 

(1)  Sublimate  on  Plaster  Per  Se. — Upon  intense  and  prolonged  igni- 
tion on  the  plaster  support,  gold  gives  a  slight  purple  to  rose  colored 
coating  near  the  assay.     It  is  best  seen  when  the  tablet  is  cold. 

(2)  Cassius  Purple  Test. — Gold  dissolves  readily  in  nitro-hydrochloric 
acid  (aqua  regia)  with  the  formation  of  auric  chloride,  AuCl3.     Evaporate 
the  solution  to  dryness  and  dissolve  the  residue  in  a  little  water.     If  a 
few  drops  of  stannous  chloride  are  now  added  a  finely  divided  precipitate 
will  form  which  is  purplish  in  transmitted  and  brownish  in  reflected 
light.     This  is  known  as  the  Cassius  purple  test  for  gold  and  is  extremely 
delicate.     The  color  is  due  to  a  mixture  of  colloidal  gold  and  tin  hydroxide. 
Ferrous  salts  also  precipitate  gold  at  ordinary  temperatures  from  neutral 
or  acid  solutions  (difference  from  platinum). 

HYDROGEN  (H) 

(1)  Water  in  Closed  Tube. — When  minerals  containing  water  of 
crystallization  or  the  hydroxyl  radicle  are  heated  in  a  closed  tube,  water 
is  set  free  which  condenses  on  the  cold  portions  of  the  tube.  More  in- 
tense heat  is  necessary  to  liberate  the  hydroxyl  radicle.  The  water 
which  may  be  neutral  towards  test  papers  is  often  acid  in  reaction,  but 
rarely  alkaline. 

IODINE  (I) 

(1)  Heating  with  Potassium  Bisulphate. — Iodides  when  heated  in  a 
closed  tube  with  KHSO4  liberate  violet  vapors,  often  accompanied  by  a 
metallic  sublimate  of  iodine. 


QUALITATIVE  BLOWPIPE  METHODS  177 

(2)  Precipitation  as  Silver  Iodide. — A  few  drops  of  AgN03  added  to  an 
iodide  in  a  dilute  HNO3  solution  precipitates  Agl,  nearly  insoluble 
in  ammonia.  (Distinction  from  Cl  and  Br.) 


IBON  (Fe) 

(1)  Magnetic  upon  Ignition. — A  few  iron  minerals  (magnetite,  pyr- 
rhotite)   are  magnetic  before  heating,   the  majority  become  magnetic 
when  heated  in  the  reducing  flame  and  allowed  to  cool.     (Cobalt  and 
nickel  minerals  react  in  a  similar  manner.) 

(2)  Borax  Bead  Test. — -In  the  oxidizing  flame  iron  colors  the  borax 
bead  yellow  when  cold.     In  the  reducing  flame  a  pale  green  results. 

(3)  Precipitation  as  Ferric  Hydroxide. — If  an  acid  solution  containing 
ferric  iron  is  made  ammoniacal  withNH4OH,  a  reddish  brown  precipitate 
of  Fe(OH)3  is  formed.     To  obtain  the  iron  in  the  ferric  condition  a  few 
drops  of  HNO3  should  be  added  to  the  HC1  when  dissolving  the  mineral. 

(4)  Test  for  Ferrous  and  Ferric  Iron. — If  an  iron  mineral  is  dissolved 
in  a  non-oxidizing  acid  as  HC1  or  H2S04,  the  valence  of  the  iron  in 
solution  will  be  the  same  as  in  the  original  mineral.     If  a  few  drops 
of  potassium  ferricyanide  are  added  to  a  solution  of  ferrous  iron,  a  dark 
blue  precipitate  will  be  formed.     Ferric  iron,  on  the  other  hand,  gives 
a  similar  precipitate  with  potassium  ferrocyanide.     Potassium  sulpho- 
cyanate,  KCNS,  gives  a  blood  red  color,  but  no  precipitate,  when  added 
to  a  ferric  solution. 

LEAD  (Pb) 

(1)  Sublimate  on  Plaster  Tablet. — When  mixed  with  bismuth  flux  and 
heated  on  a  plaster  support,  lead  minerals  yield  a  chrome  yellow  coating. 
A  drop  of  (NH4)2Sa;  applied  to  the  film  gives  a  black  spot. 

(2)  Bismuth  Flux  on  Charcoal. — Upon  charcoal  lead  minerals,  mixed 
with  bismuth  flux,  produce  a  greenish  yellow  film. 

(3)  Reduction  on  Charcoal. — Mixed  with  Na2CO3  on  charcoal  lead 
compounds  give  a  yellow  coating,  and  gray  malleable  globules. 

(4)  Precipitation  as  Lead  Sulphate. — From  a  dilute  HN03  solution 
lead  may  be  precipitated  as  white  insoluble  PbSO4,  upon  the  addition 
of  a  few  drops  of  H2S04. 

LITHIUM  (Li) 

(1)  Flame  Test. — Lithium  imparts  a  carmine  red  coloration  to  the 
flame.  The  color  is  not  as  persistent  as  that  of  strontium.  If  to  a 
solution  of  a  lithium  salt  a  few  drops  of  BaCl2  are  added,  the  red  color 
(Li)  will  appear  before  the  green  of  barium.  (Strontium  will  appear 

after  the  green.)     Lithium  minerals  do  not  become  alkaline  upon  ignition 
12 


178  MINERALOGY 

( difference  from  Sr) .     In  testing  silicates  it  is  necessary  to  mix  the  assay 
with  powdered  gypsum  and  introduce  it  into  the  flame  on  a  platinum  wire. 

MAGNESIUM  (Mg) 

(1)  Ignition     with     Cobalt    Nitrate. — Infusible     and    light    colored 
magnesium  minerals  assume  a  pink  color  when  moistened  with  a  drop 
or  two  of  cobalt  nitrate  and  intensely  ignited.     This  test  is  unsatis- 
factory at  times  and  the  following  wet  reaction  must  then  be  employed. 

(2)  Precipitation  as  Ammonium  Magnesium  Phosphate. — If  hydrogen 
sodium  phosphate,  Na2HPO4,  is  added  to  a  strongly  ammoniacal  solution, 
magnesium     is     precipitated     as    ammonium    magnesium    phosphate, 
NH4MgP04.     The  precipitate  is  white  and  crystalline,  and  may  appear 
only  after  shaking  and  standing  for  a  short  time.     In  order  to  remove 
interfering  elements  proceed  as  follows:  The  HC1  solution  containing  a 
few  drops  of  HNO3  is  boiled  and  then  made  alkaline  with  NH4OH. 
This  will  precipitate  Fe,  Al,  and  Cr,  if  present.     To  the  ammoniacal 
filtrate  add  ammonium  oxalate  to  remove  Ca,  Ba,  and  Sr.     To  the  filtrate 
Na2HP04  is  then  added  to  test  for  magnesium. 

MANGANESE  (Mn) 

(1)  Borax   Bead    Test. — Manganese    colors   the  borax  bead  reddish 
violet  in  the  oxidizing  flame,  but  becomes  colorless  in  the  reducing  flame. 
Salt  of  phosphorus  gives  a  similar  reaction  but  the  test  is  not  as  sensitive. 

(2)  Fusion  with  Sodium   Carbonate  on  Platinum  Wire. — When  dis- 
solved in  a  Na2CO3  bead  in  the  oxidizing  flame,  manganese  compounds 
color  the  fusion  a  bluish  green  due  to  the  formation  of  sodium  manganate, 
Na2MnO4.     If  a  charcoal  support  is  used  instead  of  platinum  wire,  a 
small  amount  of  KNO3  should  be  added  to  the  Na2C03  to  offset  the 
reducing  action  of  the  support. 

(3)  Heating  in  Closed  Tube. — Some  of  the  higher  oxides  yield  oxy- 
gen, or  when  dissolved  in  HC1  evolve  chlorine. 

(4)  Oxidation   to  Permanganic   Acid. — Boil   with  HNO3  and  Pb304 
and  allow  the  lead  oxide  to  settle.     The  supernatant  solution  will  be 
purplish  from  the  permanganic  acid  formed. 

MERCURY  (Hg) 

(1)  Sublimate  on  Plaster  Tablet. — When  mixed  with  bismuth  flux  and 
heated  on  a  plaster  support,  mercury  minerals  produce  a  coating  which 
is  usually  a  combination  of  scarlet,  yellow,  and  greenish  black. 

(2)  Heating  in  a  Closed  Tube. — When  mixed  with  three  parts  of  dry 
Na2CO3  and  heated,  metallic  mercury  will  be  volatilized  and  condensed 
as  globules  on  the  sides  of  the  tube. 


QUALITATIVE  BLOWPIPE  METHODS  179 

(3)  Precipitation  by  Copper. — A  clean  copper  wire  immersed  in  a 
mercury  solution  becomes  covered  with  a  deposit  of  metallic  mercury. 

MOLYBDENUM  (Mo) 

(1)  Sublimate  on  Plaster  and  Charcoal. — When  heated  per  se  with  the 
oxidizing  flame  some  molybdenum  compounds  yield  MoO3,   which  is 
3^ellow  when  hot  and  white  when  cold.     When  touched  with  the  reducing 
flame  the  white  coating  is  changed  to  a  deep  blue.     If  a  charcoal  support 
is  used,  a  copper  red  sublimate  will  also  be  noted  surrounding  the  assay 
which  is  best  seen  in  reflected  light. 

(2)  Treatment  with  Concentrated  Sulphuric  Acid. — If  a  molybdate  is 
treated  with  a  few  drops  of  concentrated  H2SO4  in  a  porcelain  dish  and 
evaporated  almost  to  dryness,  the  mass  upon  cooling  is  colored  intensely 
blue.     The  color  will  disappear  upon  the  addition  of  water.     Molyb- 
denite (MoS2)  must  be  oxidized,  either  by  boiling  to  dryness  with  HNO3 
or  by  roasting,  before  it  can  be  tested  in  this  manner. 

(3)  Formation  of  Molybdenum  Thiocyanate. — KCNS  causes  little  or 
no  change  when  added  to  HC1  solution  of  molybdenum,  but  if  it  is  then 
treated  with  zinc  or  SnCl2,  a  blood  red  coloration  is  produced.     The 
reaction  takes  place  in  the  presence  of  phosphoric  acid  (difference  from 
iron).     If  H2O2  is  added  to  the  solution  immediately  after  the  red  color 
has  developed,  the  color  disappears,  returning  as  soon  as  the  H2O2  has 
been  reduced. 

NICKEL  (Ni) 

(1)  Bead  Tests. — Nickel  colors  the  borax  bead  in  the  oxidizing  flame  a 
reddish  brown,  while  the  salt  of  phosphorus  bead  is  yellow. 

(2)  Pale  Blue  Solution  with  Ammonium  Hydroxide. — A  fairly  concen- 
trated acid  solution  of  Ni  will  become  pale  blue  upon  adding  an  excess  of 
NH4OH.     The  color  is  not  as  dark  a  shade  as  that  produced  by  copper. 

(3)  Precipitation   with  Dimethylglyoxime. — Dissolve   the   mineral    in 
HNO3  and  make  the  solution  alkaline  with  NH4OH.     Filter  if  necessary 
and  to  the  filtrate  add  several  cc.  of  an  alcoholic  solution  of  dimethyl- 
glyoxime.     A  scarlet  precipitate  indicates  nickel. 

NIOBIUM  (Nb) 

(1)  Reduction  with  Tin.  Finely  powdered  niobates  are  decomposed 
when  heated  to  dull  redness  with  KHSO4  in  a  test  tube.  When  decom- 
position is  complete,  rotate  and  incline  the  tube  so  that  the  melt  may 
solidify  as  a  thin  crust  on  the  sides.  Add  HC1,  some  metallic  tin,  and  boil. 
Reduction  takes  place  and  a  light  blue  color  due  to  niobium  will  appear. 
The  color  becomes  much  fainter  upon  the  addition  of  water. 


180  MINERALOGY 

NITROGEN  (N) 

(1)  Heating  in  Closed  Tube. — Nitrates  heated  in  a  closed  tube  with 
KHSO4  liberate  reddish  brown  fumes  of  NO2. 

(2)  Brown  Ring  Test. — Acidify  the  solution  with  a  few  cc-  of  dilute 
H2S04,  then  add  twice  its  volume  of  concentrated  H2S04.     Cool  and  add 
fresh  FeSO4  solution  so  that  it  forms  a  separate  layer  on  top.     A  brown 
ring  will  form  at  the  junction  of  the  two  liquids.     (Iodides  give  a  ring 
of  free  iodine  which  interferes  with  the  test.) 

OXYGEN    (O) 

(1)  Heating  in  Closed  Tube. — Some  of  the  higher  oxides  liberate 
oxygen  which  causes  a  glowing  splinter  to  take  fire. 

(2)  Evolution  of  Chlorine. — If  HC1  is  added  to  some  of  the  higher 
oxides,  free  chlorine  is  liberated  which  is  recognized  by  its  odor  and 
bleaching  properties. 

PHOSPHORUS    (P) 

(1)  Reduction  with    Magnesium    Ribbon. — Phosphides  of  aluminum 
and  the  heavy  metals  should  be  fused  with  Na2C03  and  the  powdered 
fusion  ignited  in  a  test  tube  with  Mg  ribbon.     The  phosphorus  is  con- 
verted into  a  phosphide  which  upon  the  addition  of  a  few  drops  of  water 
liberates  phosphine,  PH3,  recognized  by  its  unpleasant  garlic  odor  and 
ability  to  produce  a  black  coloration  when  brought  in  contact  with  filter 
paper  moistened  with  AgNO3.     Phosphates  of  the  alkalies  and  alkaline 
earths  may  be  ignited  with  Mg  ribbon  directly  without  previous  fusion. 
This  test  is  not  satisfactory  if  arsenic  or  antimony  are  present. 

(2)  Precipitation    with    Ammonium    Molybdate. — The   phosphate   is 
dissolved  in  HNOs  (if  insoluble,  fusion  with   Na2CO3  should  precede 
solution  in  acid)  and  a  portion  of  the  filtrate  added  to  an  excess  of  ammo- 
nium molybdate  solution.     Upon  standing  or  slightly  warming  a  yellow 
precipitate  of  ammonium  phosphomolybdate  will  be  formed. 

PLATINUM   (Pt) 

(1)  Brownish  Red  Solution  with  Potassium  Iodide. — Dissolve  several 
scales  of  platinum  in  concentrated  aqua  regia  and  evaporate  to  dryness. 
Redissolve  in  HC1  and  evaporate  to  a  thick  paste.     Dilute  with  water 
and  then  add  a  few  drops  of  H2SO4  and  a  crystal  of  KI,     The  solution 
assumes  a  wine  red  color.     This  test  will  not  detect  traces  of  platinum 
in  the  presence  of  large  quantities  of  iron. 

(2)  Precipitation   of  Potassium  Platinic   Chloride. — Add   KC1   to   a 
portion   of  the  paste  obtained  as  indicated  in  (1).     Yellow  crystals  of 
K2PtCl6,  insoluble  in  alcohol,  will  be  precipitated. 


QUALITATIVE  BLOWPIPE  METHODS  181 

POTASSIUM    (K) 

(1)  Flame  Test. — Volatile  potassium  compounds  impart  a  pale  violet 
color  to  the  non-luminous  flame.  If  obscured  by  sodium,  view  the 
flame  through  a  thick  blue  glass  or  a  Merwin  Color  Screen.  Through 
blue  glass  the  flame  appears  purplish  red,  while  through  the  Merwin 
screen  the  coloration  is  blue  violet  through  division  1,  and  red  violet 
through  divisions  2  and  3.  In  testing  silicates  it  will  be  necessary  to 
mix  the  assay  with  powdered  gypsum  and  introduce  it  into  the  flame  on 
a  platinum  wire. 

SELENIUM  (Se) 

(1)  Sublimate  on  Plaster  Tablet. — When  heated  on  the  plaster  tablet 
per  se,  selenium  gives  a  coating  which  is  cherry  red  to  crimson  in  thin 
layers  and  nearly  black  in  thick  deposits.     When  volatilized  the  fumes 
are  reddish  and  have  the  odor  of  rotten  horse-radish. 

(2)  Flame  Test. — When  volatilized-selenium  imparts  an  indigo  blue 
coloration  to  the  flame. 

SILICON  (Si) 

(1)  Salt  of  Phosphorus  Bead. — Silica  does  not  dissolve  readily  in  the 
salt  of  phosphorus  bead  but  forms  an  insoluble  translucent  skeleton. 

(2)  Gelatinization  with  Acid. — Finely  powdered  silicates,  which  are 
completely  soluble  in  HNO3  or  HC1,  form  a  gelatinous  mass  of  silicic  acid 
when  evaporated  almost  to  dryness. 

(3)  Fusion  with  Sodium  Carbonate. — Insoluble  silicates  should  be  fused 
with  three  to  four  parts  of  Na2CO3  and  dissolved  in  HC1.     Evaporate  to 
complete  dryness  and  redissolve  the  bases  with  fairly  concentrated  HC1. 
SiO2  remains  insoluble  and  may  be  removed  by  filtering  the  solution. 

SILVER  (Ag) 

(1)  Reduction  on   Charcoal. — When   silver  minerals    are    heated  on 
charcoal  with  three  parts  of  Na2CO^  they  are  readily  reduced  to  malleable, 
metallic  globules.     If  sulphur,  arsenic,  or  antimony  are  present,  roasting 
should  precede  reduction  in  order  to  volatilize  these  constituents. 

(2)  Precipitation  as  Silver  Chloride. — If  to  a  HN03  solution  of  a  silver 
mineral  a  few  drops  of  HC1  are  added,  a  white  curdy  precipitate  of  AgCl 
will  be  formed.     This  precipitate  is  soluble  in  ammonia. 

SODIUM  (Na) 

(1)  Flame  Test. — Sodium  imparts  an  intense  and  prolonged  yellow 
color  to  the  flame.  The  color  is  invisible  through  a  thick  dark  blue  glass 


182  MINERALOGY 

or  the  Merwin  Screen.     Silicates  of  sodium  should  be  mixed  with  gypsum 
and  introduced  into  the  flame  on  a  platinum  wire. 

STRONTIUM  (Sr) 

(1)  Flame  Test. — Strontium  imparts  a  crimson  color  to  the  flame, 
which  is  more  persistent  than  that  of  Li,  and  is  invisible  through  division 
1  of  the  Merwin  screen  (distinction  from  Ca).     If  a  few  drops  of  BaCl2 
are  added  to  a  solution  of  a  Sr  salt  the  red  color  (Sr)  will  appear  after  the 
green  of  Ba.     (Li  will  appear  before  the  green.) 

(2)  Alkaline  Reaction  upon  Ignition. — With  the  exception  of  silicates 
and  phosphates,  strontium  minerals  give  upon  ignition  an  alkaline  re- 
action with  turmeric  paper.     (Distinction  from  Li.) 

(3)  Precipitation  as  Strontium  Sulphate. — From  a  Sr  bearing  solution 
SrS04  is  precipitated  upon  the  addition  of  a  few  drops  of  dilute  H2SO4. 
(Distinction  from  Li.) 

SULPHUR  (S) 

When  present  as  sulphides: 

(1)  Heating  in  Open  Tube. — Powdered  sulphides  are  oxidized  when 
heated  in  an  open  tube.     SO2  is  set  free  and  is  recognized  by  its  pungent 
odor  and  acid  reaction  with  litmus  paper. 

(2)  Heating  in   Closed   Tube. — When  heated  in  a  closed  tube  some 
sulphides  liberate  a  portion  of  their  sulphur  which  condenses  as  a  dark  red 
liquid  when  hot  and  changes  to  a  crystalline  yellow  solid  when  cold. 

(3)  Fusion  with  Sodium  Carbonate. — Fuse  with  three  to  four  parts  of 
Na2CO3  and  place  a  portion  of  the  fusion  on  a  silver  coin.     Moisten  with 
a  few  drops  of  water.     A  dark  brown  to  black  spot  indicates  sulphur, 
provided  selenium  and  tellurium  are  absent.     To  another  portion  of  the 
fusion  placed  in  a  watch  glass,  add  several  drops  of  water  and  a  drop  or 
two  of  freshly  prepared  sodium  nitroferricyanide.     An  intense  purple 
color  is  indicative  of  sulphur. 

(4)  Oxidation  with  Nitric  Acid. — Hot  concentrated  HNO3   oxidizes 
sulphides  to  sulphates,  liberating  some  free  sulphur  which  rises  to  the 
surface.     A  few  drops  of  BaCl2  added  to  the  filtrate  precipitates  the 
sulphur  as  white  BaSO4. 

When  present  as  sulphates: 

(5)  Fusion  with  Sodium  Carbonate. — Mix  the  sulphate  with  an  equal 
volume  of  powdered  charcoal  and  three  volumes  of  Na2CO3.     Fuse  and 
test  as  indicated  in  (3). 

(6)  Precipitation    as   Barium   Sulphate. — Sulphates   soluble   in    HC1 
are  precipitated  as  BaSO4  upon  the  addition  of  BaCl2. 

TELLURIUM  (Te) 

(1)  Sublimate  on  Plaster  Tablet. — Tellurides   heated  per  se  or  with 
bismuth  flux  on  a  plaster  support  yield  a  purplish  brown  coating.     A 


QUALITATIVE  BLOWPIPE  METHODS  183 

drop  of  concentrated  H2SO4  added  to  the  film  and  gently  heated  forms  a 
pink  spot. 

(2)  Sublimate  on  Charcoal. — When  heated  on  charcoal  a  white  sub- 
limate of  TeO2  is  formed  near  the  assay  which  resembles  Sb203.     The 
coating  is  volatile  and  when  touched  with  the  reducing  flame  it  colors 
the  flame  a  pale  green. 

(3)  Test  with  Concentrated  Sulphuric  Acid. — When  gently  warmed 
with  concentrated  H2SO4  powdered  tellurides  produce  a  reddish  violet 
solution.     Too  intense  heat  or  the  addition  of  water  will  cause  the  color 
to  disappear. 

TIN  (Sn) 

(1)  Reduction  on  Charcoal. — If  fused  with  an  equal  volume  of  pow- 
dered charcoal  and  two  volumes  of  Na2CO3,  tin  minerals  are  reduced, 
forming  minute  metallic  globules.     Upon  prolonged  ignition  the  tin  is 
volatilized  and  deposits  as  a  white  coating  of  SnO2.     Add   a  drop  of 
Co(NO3)2  to  the  coating  and  heat.     A  bluish  green  spot  results. 

(2)  Reduction  by  Hydrogen. — Place  a  fragment  of  cassiterite  (SnO2)  in 
contact  with  metallic  zinc  and  add  dilute  HC1.     H2  is  liberated  and  re- 
duces the  SnO2.     The  mineral  becomes  coated  with  a  thin  layer  of  metal- 
lic tin. 

TITANIUM  (Ti) 

(1)  Reduction  with  Tin. — After  fusion  with  three  volumes  of  Na2CO3, 
the  titanium  will  dissolve  in  HC1  forming  TiCl4.     Upon  boiling  with 
metallic  tin  the  titanium  is  reduced  to  TiCl3,  the  solution  assuming 
a  violet  color.     If  only  a  small  amount  of  titanium  is  present  test  No. 
2  should  be  employed. 

(2)  Oxidation  with  Hydrogen  Peroxide. — Dissolve  the  Na2CO3  fusion 
in  1  : 1  H2SO4  and  when  cold  add  water  and  a  few  drops  of  H202.     The 
solution  is  colored  a  pale  yellow  to  orange  red,  depending  upon  the  amount 
of  Ti  in  the  solution.   'This  reaction  depends  upon  the  formation  of 
TiO3.  x  H2O  and  is  exceedingly  delicate. 

TUNGSTEN  (W) 

(1)  Reduction  with  Tin. — After  fusion  with  Na2CO3,  the  sodium 
tungstate  is  dissolved  in  hot  water  (niobates  are  insoluble  in  water). 
Filter  if  necessary  and  acidify  the  filtrate  with  HC1.  An  insoluble  white 
precipitate  of  hydrated  tungstic  acid,  H2WO4.H2O,  is  formed  in  the  cold, 
which  upon  boiling  turns  yellow  (H2WO4).  Upon  adding  metallic  tin 
and  boiling,  a  dark  blue  solution  results  which  is  due  to  a  heavy  pre- 
cipitate (WO 3  -f  WO2)  held  in  suspension.  Dilution  with  water  will  not 


184  MINERALOGY 

cause  the  color  to  disappear   (Distinction  from  niobium).     Prolonged 
reduction  finally  produces  a  brown  color  (WO2). 

URANIUM   (U) 

(1)  Salt  of  Phosphorus  Bead. — Uranium  colors  the  salt  of  phosphorus 
bead  a  yellowish  green  in  the  oxidizing  flame  and  a  bright  green  in 
the  reducing  flame.     In  the  borax  bead  uranium  can  not  be  distinguished 
from  iron. 

(2)  Precipitation  as  Potassium  Uranate. — Potassium  ferrocyanide  pro- 
duces a  brown  precipitate  (UO2)2  [Fe(CN)6]  in  a  slightly  acid  solution, 
which  upon  the  addition  of  KOH  is  changed  to  the  yellow  potassium 
uranate,   K2U2O7      (Distinction  from  cupric  ferrocyanide.)     If  iron  is 
present  proceed  as  follows:  Dissolve  the  fusion  in  aqua  regia.     Make 
alkaline  with  NH4OH  which  will  precipitate  the  Fe  and  U  as  Fe(OH)3 
and   (NH4)2U207.     Add   (NH4)2C03  and  shake,  the  uranium  forms    a 
soluble    complex   salt.     Filter   and   acidify   with    HC1.     Add    NH2OH 
until  alkaline  and  the  uranium  is  precipitated  free  from  iron.     Test 
precipitate  as  indicated  in  (1). 

VANADIUM   (V) 

(1)  Bead  Tests. — Vanadium  can  usually  be  detected    by  the  bead 
colorations.     In  the  borax  bead  the  color  is  yellowish  green  in  the  oxi- 
dizing flame  and  emerald  green  in  the  reducing  flame,  while  the  micro- 
cosmic  salt  bead  is  colored  light  yellow  and  emerald  green  respectively. 

(2)  Oxidation  with  Hydrogen  Peroxide. — If  to  an  acid  solution  of  a 
vanadate  H2O2  is  added,  pervanadic  acid,  HVO4,  is  formed  which  colors 
the  solution  a  reddish  brown.     This  is  a  very  delicate  reaction. 

(3)  Reduction  with  zinc. — Zinc  in  an  acid  medium  causes  reduction  of 
vanadic  acid  so  that  the  solution  turns  blue,  then  green,  and  finally 
violet.     (This  test  is  not  as  delicate  as  test  No.  2.) 

ZINC   (Zn) 

(1)  Sublimate  on  Charcoal. — When  the  finely  powdered  mineral   is 
mixed  with  Na2CO3  and  a  small  amount  of  charcoal,  zinc  is  reduced  and 
then  quickly  oxidized  forming  an  oxide  coating  near  the  assay  which  is 
pale  yellow  when  hot,  white  when  cold.     A  drop  of  Co(NO3)2  added  to 
the  sublimate  and  heated  produces  a  green  spot. 

(2)  Heating  with  Cobalt  Nitrate. — When  moistened  with  a  drop  of 
cobalt  nitrate  and  intensely  ignited,  infusible  and  light  colored  silicates  of 
zinc  usually  assume  a  blue  color.     ZnO  or  minerals  forming  the  oxide 
upon  heating,  such  as  ZnC03,  become  green. 


QUALITATIVE  BLOWPIPE  METHODS  185 

ZIRCONIUM  (Zr) 

(1)  Turmeric  Paper  Test. — Fuse  with  Na2C03  and  dissolve  in  dilute 
HC1.     Turmeric  paper  dipped  in  this  solution  and  dried  is  colored  reddish 
brown.     (See  boron.)     It  is  well  to  compare  the  turmeric  paper  with 
another  strip  treated  only  with  HC1  and  dried. 

(2)  Precipitation  as  Phosphate  in  Acid  Solution. — Dissolve  the  Na2CO3 
fusion  in  HC1,  boil,  and  filter.     To  the  acid  filtrate  add  several  drops  of 
Na2HPO4  and  a  white  precipitate  of  zirconium  phosphate  will  be  formed. 
(Titanium  is  likewise  precipitated  under  similar  conditions.) 


CHAPTER  XIV 

DESCRIPTIVE  MINERALOGY 
INTRODUCTION 

Descriptive  mineralogy  includes  a  detailed  discussion  in  some  sys- 
tematic order  of  the  crystallographic,  physical,  and  chemical  properties 
of  minerals.  Characterizing  features,  associations,  occurrences,  and 
uses  are  also  given.  Two  general  methods  of  classification  of  minerals 
are  in  common  use.  In  one  of  these  methods,  all  minerals  possessing 
some  element  as  an  important  constituent  are  grouped  together  ir- 
respective of  their  chemical  and  crystallographic  relationships.  Thus, 
the  important  iron  minerals  would  be  grouped  together,  as  follows: 


1.  Pyrrhotite, 

2.  Pyrite, 

3.  Hematite, 


FeS 
FeS2 
Fe203 


4.  Magnetite, 

5.  Limonite, 

6.  Siderite, 


Fe(FeO2)2 

Fe2O3-H2O, 

FeC03 


The  second  method  of  classification  is  considered  more  scientific, 
and  is  followed  in  this  text,  the  minerals  being  grouped  according  to  their 

chemical  composition  and  the  principle  of 
isomorphism.  Minerals  with  the  simplest  com- 
position are  discussed  first,  while  those  of 
greatest  complexity  are  treated  last.  Nine 
classes  are  easily  arranged. 

1.  Elements. 

2.  Sulphides,  arsenides,  sulpho-minerals. 

3.  Oxides,  hydroxides. 

4.  Haloids. 

5.  Nitrates,  carbonates,  manganites. 

6.  Sulphates,    chromates,    molybdates,   tungstates, 
uranates. 

7.  Aluminates,  borates,  ferrites. 

8.  Phosphates,  vanadates. 

9.  Silicates,  titanates. 

Within  each   of  these   classes  the  various 


FIG.  393.  —  James  D. 
Dana  (1813-1895).  Profes- 
sor in  Yale  University  (1850- 
1890).  Author  of  "System 
of  Mineralogy,"  the  standard 


reference  work  on  descriptive    minerals  are   arranged,  as  far  as   possible,   in 

mineralogy.  .  ...  ., 

isomorphous    series,    thus    bringing    together 

those  minerals  with  analogous  chemical  compositions  and  strikingly 
similar  crystal  forms.  In  all,  one  hundred  fifty  minerals  are  described. 
The  one  hundred  minerals,  which  are  considered  as  the  most  important 
are  designated  by  large,  heavy  type,  thus  QUARTZ.  For  the  remaining 

186 


DESCRIPTIVE  MINERALOGY 


187 


fifty  minerals  smaller  type  is  used,  thus  Scheelite.  In  describing  the 
individual  minerals,  the  following  order  is  used :  a,  Name  and  formula; 
b,  Crystallographic  features  and  structure;  c,  Important  physical  properties, 
such  as  cleavage,  fracture,  hardness,  specific  gravity,  luster,  color,  etc.;  d, 
Chemical  composition  and  properties;  e,  Varieties,  if  important;  f ,  Occur- 
rence, associations,  and  important  localities;  g,  Uses. 


Fio.    394. — Alfred     Lacroix      (1863  — ).     Professor     of      mineralogy   in     the     Museum 
d'  Historic  Naturelle  de  France,  Paris  (J893  — ).     Authority  on  the  minerals  of  France. 


I.    ELEMENTS 

Of  the  eighty  and  more  known  elements,  only  the  following  nine 
occur  uncombined  in  nature  in  sufficient  quantities  to  warrant 
description : 

NON-METALS 

Cubic 
Hexagonal 


DIAMOND,  C 
GRAPHITE,  C 
SULPHUR,  S 


Arsenic,  As 
Bismuth,  Bi 

PLATINUM,  Pt 

COPPER,  Cu 
SILVER,  Ag 
GOLD    Au 


SEMI-METALS 
ARSENIC  GROUP 

METALS 
COPPER  GROUP 


Orthorhombic 


Hexagonal 
Hexagonal 

Cubic 

Cubic 
Cubic 
Cubic 


The  specific  gravities  of  the  non-metals  are  low,  those  of  the  semi- 
metals  range  from  5.6  to  10,  while  those  of  the  metals  may  be  as  high  as 
22.  The  metals  are  malleable  and  ductile. 


188  MINERALOGY 

Non-metals 

The  three  minerals  to  be  described  here  are  of  great  value  in  commerce 
and  industry. 

DIAMOND,  Bortz,  Carbonado,  C. 

Cubic,  probably  hexoctahedral  class.  Usually  in  crystals  or  crystal 
fragments,  microscopically  small  or  over  3,000  carats*  in  weight.  Most 
common  forms  are  the  octahedron  (Fig.  395),  rhombic  dodecahedron, 
and  hexoctahedron;  rarer,  the  cube.  Crystals  are  often  rounded  and 
distorted.  Contact  twins  according  to  the  Spinel  law,  the  twinning 
plane  being  parallel  to  a  face  of  the  octahedron,  are  frequently  noted. 
Sometimes  massive. 

Highly  perfect  octahedral  cleavage.  Hardness,  10  (hardest  known 
mineral).  Specific  gravity,  3.15  to  3.53.  Greasy  adamantine  luster 
(carbonado,  dull) .  Commonly  colorless,  or  slightly 
yellowish;  also  yellow,  red,  green,  blue;  more  rarely 
black.  Transparent  to  translucent  and  opaque. 
Very  high  index  of  refraction  (nB  une  =  2.407, 
nDiine  =  2.417,  naune  =  2.465).  The  fire  so  char- 
acteristic of  the  diamond  is  due  to  the  exception- 
ally strong  dispersion  (2.465  -  2.407  =  0.058). 
Transparent  to  X-rays,  while  lead  glass  imitations, 
such  as  paste  and  strass,  are  not.  Some  diamonds 


FIG.  395.— Diamond    phosphoresce    after    exposure  to  light  or  electric 

in    blue    ground.     Kim-     *!.       ^ 
berley,  South  Africa.  discharges. 

Colorless  diamonds  are  pure  carbon,  for  on  com- 
bustion in  an  atmosphere  of  oxygen  only  carbon  dioxide  is  obtained. 
Colored  stones  yield  small  residues.  Unaffected  by  acids.  Inclusions, 
especially  of  carbonaceous  matter,  are  frequent. 

There  are  three  varieties  of  the  diamond,  (1)  Diamond  proper,  (2) 
Bortz  or  bort,  and  (3)  Carbonado. 

1.  Diamond  Proper. — This  variety  has  been  known  from  the  earliest 
times,  and  was  called  adamas  by  the  ancients.  These  older  stones  were 
obtained  from  secondary  deposits  in  eastern  and  southern  India,  which 
localities  furnished  some  of  the  world's  famous  diamonds,  but  their 
output  at  present  is  very  small. 

According  to  tradition,  diamonds  were  first  discovered  in  the  gold 
washings  in  Brazil  in  1670,  but  not  positively  identified  as  such  until 
1721.  The  provinces  of  Minas  Gerses  and  Bahia  are  the  most  important 
producers.  Here  also  diamonds  occur  in  stream  sands  and  gravels. 

The  most  important  locality,  yielding  at  present  about  95  per  cent, 
of  the  world's  production,  is  South  Africa  where  diamonds  were  dis- 
covered in  1867  on  the  south  shore  of  the  Orange  river  near  Hopetown. 

*  The  metric  carat  is  200  milligrams,  and  has  been  in  use  in  the  United  States 
since  July  1,  1913. 


DESCRIPTIVE  MINERALOGY 


189 


Yellow 


FIG.  396. — Sertion  through 
the  Kimberley  Mine. 


At  first,  they  were  found  in  the  Driver  diggings,"  that  is,  in  the  sands  and 
gravels  of  the  streams,  especially  the  Orange,  Vaal,  and  Modder  rivers. 
About  three  years  later,  diamonds  were  discovered  in  primary  deposits, 
known  as  "dry  diggings,"  upon  the  plateau  between  the  Vaal  and  Modder 
rivers.  Here  the  occurrence  of  the  diamond  is  restricted  to  limited  areas, 
elliptical  or  circular  in  outline,  and  varying  from  20  to  700  and  more 
meters  in  diameter  (Figs.  396  and  397).  On 
the  surface  the  diamonds  were  found  in  a  soft, 
decomposed  material  known  as  the  yellow 
ground.  At  depth  the  diamond-bearing  areas 
constrict,  and  the  yellow  ground  is  underlaid 
by  a  hard  basic  magnesian  rock,  known  as 
kimberlite  or  the  blue  ground.  These  areas 
are  volcanic  pipes.  Originally  the  diamonds 
were  easily  recovered  from  the  soft  yellow 
ground  by  simply  washing  away  the  lighter 
constituents,  and  sorting  the  diamonds  from  the 
concentrates.  But  now,  the  harder  blue  ground  is  brought  to  the  surface 
in  large  lumps  and  generally  exposed  in  the  open  fields,  "depositing 
floors,"  to  the  action  of  the  atmospheric  agencies.  In  due  time  the 
material  crushes  very  easily,  and  is  then  washed  and  concentrated. 
These  concentrates  are  passed  over  oscillating  tables  covered  with 
grease,  called  "sorters  or  pulsators."  Of  all  the  minerals  in  the  concen- 
trates the  diamond  is  the  only  one  which 
will  stick  to  the  grease,  from  which  it  is 
easily  recovered  at  intervals.  At  the  Pre- 
mier mine  the  blue  ground  is  crushed  and 
concentrated  immediately  after  being  mined. 
Kimberley  is  the  diamond  center  for 
South  Africa,  four  important  mines,  the 
Kimberley,  Du  Toitspan,  De  Beers,  and 
Bultfontein,  being  located  in  its  immediate 
vicinity.  Other  important  mines  are  the 
Jagersfontein,  in  the  Orange  Free  State, 
and  the  Premier  in  the  Transvaal,  near 
Pretoria.  The  Premier  is  the  largest  known 
diamond  mine  and  covers  about  eighty  acres. 
Diamonds  also  occur  in  secondary  deposits 
near  Ltideritz  Bay  on  the  west  coast  of 
Africa,  and  along  the  Kasai  river  in  the  Belgian  Congo.  In  1913  the 
various  African  localities  produced  over  5%  million  carats  of  diamonds 
valued  at  about  $45,000,000. 

Diamonds  have  also  been  found  in  Australia,  Ural  Mountains,  British 
Guiana,  Columbia,  Mexico,  and  British  Columbia.     In  the  United  States 


FIG.  397. — Kimberley  Open  Dia- 
mond Mine,  Depth  1000  feet. 


190 


MINERALOGY 


occasional  diamonds  have  been  discovered  in  Wisconsin,  Indiana,  Michi- 
gan, California,  Georgia,  and  North  Carolina.  The  most  important 
find  of  diamonds  in  the  United  States  was  made  on  August  1,  1906, 
near  Murfreesboro,  Pike  County,  Arkansas.  The  occurrence  here  is 
strikingly  similar  to  that  of  the  principal  South  African  localities,  and 
up  to  July  1,  1916,  more  than  4,500  stones  have  been  recovered. 


FIG.  398. 


FIG.  399. 


FIG.  400. 


Microscopic  diamonds  have  been  found  in  meteorites  (Canon  Diablo, 
Arizona)  and  in  certain  types  of  steel  and  cast  iron. 

The  diamond  has  long  been  used  as  a  gem,  but  the  ancients  were 
content  to  polish  the  natural  crystal  faces.  In  1456  the  art  of  cutting 
facets  on  the  diamond  was  invented  whereby  the  fire  was  greatly  in- 


FIG.  40L-r-Cullinan    Diamond.     Premier    Mine,    South    Africa.     Weight    3,106    carats. 

creased.  Many  different  styles  of  cutting  have  been  in  use  at  various 
times,  but  at  present  the  brilliant  cutting  is  the  most  common.  As 
illustrated  in  Fig.  398,  the  octahedron,  either  natural  or  obtained  by 
cleavage,  is  made  the  basis  for  this  style  of  cutting.  Figures  399  and  400 
are  side  and  top  views  of  the  cut  stones.  Usually  there  are  58  facets, 


DESCRIPTIVE  MINERALOGY 


191 


but  in  some  cases  as  high  as  74  are  cut.  Depending  upon  the  character 
of  the  rough  stone,  from  a  third  to  one-half  of  its  weight  is  lost  in  cutting 
Amsterdam  and  Antwerp  are  the  most  important  diamond  cutting  cen- 
ters. See  also  pages  329  to  338. 

The  largest  diamond  ever  found  was  the  Cullinan  or  Premier,  also 
called  the  "Star  of  Africa,"  discovered  on  January  25,  1905,  at  the  Pre- 


9     ft 


FIG.  402. — The  nine  largest  stones  cut  from  the  Cullinan  Diamond. 

mier  mine,  in  the  Transvaal  (Fig.  401).  This  stone  weighed  621.2 
grams  or  3,106  carats.  It  measured  about  10  X  6.5  X  5  centimeters, 
and  was  a  cleavage  fragment  of  a  larger  stone.  It  was  purchased  by  the 
Assembly  of  Transvaal  and  presented  to  King  Edward  VII  and  subse- 
quently cut  into  9  larger  (Fig.  402)  and  96  smaller  stones.  The  two 
largest  stones  are  called  Cullinan  I  and  II,  and  weigh  530.2  and  317.4 
carats,  respectively.  Some  of  the  other  famous  cut  diamonds  and  their 


FIG.  403. — Photograph  of  glass  models  of  famous  large  diamonds. 

approximate  weights  are:  the  Jubilee,  245.3  carats;  Kohinoor,  106 
carats;  Orloff,  195  carats;  Regent,  137  carats;  Tiffany  (yellow),  128.5 
carats;  Hope  (blue),  44.5  carats;  Dresden  (green),  40  carats;  Star  of 
the  South,  125.5  carats  (Fig.  403). 

(2)  Bortz. — Also  called  bort  and  boart.     Dark  colored,  poorly  crystal- 
lized   variety,    often  with  a  radial  fibrous  structure.     Translucent  to 


192 


MINERALOGY 


opaque.     Crystals  and  fragments  of  an  inferior  quality,  hence,  unfit  for 
gem  purposes,  are  also  called  bortz. 

(3)  Carbonado. — Often  called  black  diamond,  or  simply  carbon. 
This  variety  is  compact,  opaque,  and  usually  black  to  gray  in  color  (Fig. 
404).  Specific  gravity,  3.15  to  3.29.  No  cleavage.  Found  in  placer 
deposits  in  the  Province  of  Bahia,  Brazil.  The  largest  carbonado  ever 
found  weighed  3,078  carats. 


FIG.  404. — Carbonado.     Brazil. 


FIG.  405.— Diamond  drill  bit. 


Diamond  proper  is  used  extensively  as  a  gem.  Inferior  stones  and 
bortz  are  used  as  an  abrasive,  glass  cutters,  and  as  dies  for  wire-drawing. 
Carbonado,  broken  into  small  cubes,  is  used  in  diamond  drilling,  the  small 
cubes  being  set  in  the  bit  (Fig.  405).  Diamond  drilling  is  used  exten- 
sively to  determine  the  location  and  size  of  ore  bodies  and  the  character 
of  the  rocks  to  be  penetrated  and,  hence,  is  of  the  utmost  importance  in 

mining  and  structural  engineering. 


GRAPHITE  (Plumbago,  Black  Lead],  C. 
Hexagonal,  ditrigonal  scalenohedral 
class.  Crystals  are  small,  tabular,  and 
hexagonal  in  outline,  but  very  rare. 
Usually  found  in  foliated,  scaly,  granu- 
lar and  compact,  or  earthy  masses  (Fig. 
406). 

Perfect  basal  cleavage,  yielding  very 
thin  and  flexible  laminae.  Hardness  1 
to  2,  marks  paper  and  soils  the  fingers. 
Greasy  feel.  Specific  gravity  1.9  to  2.3. 
Iron  black  to  dark  gray  in  color.  Shiny 

black  streak.     (Rubbed  streak  black;  molybdenite,  greenish.)     Opaque. 

Metallic  luster,  sometimes  dull  or  earthy.     Good  conductor  of  electricity. 

Transparent  to  the  X-rays. 

Essentially  carbon,  but  not  as  pure  as  the  diamond.     On  combustion 

may  yield  as  much  as  20  per  cent.  ash.     Not  attacked  by  acids.     Graphite 

brought  in  contact  with  metallic  zinc  in  a  solution  of  copper  sulphate 

is  quickly  copper  plated,  while  molybdenite  treated  in  the  same  way  is 

only  slowly  coated.     Infusible. 


FIG.  406.— Graphite  with  calcite. 
Ticonderoga,  New  York. 


DESCRIPTIVE  MINERALOGY 


193 


Graphite  occurs  in  large  masses  and  disseminated  scales,  also  in 
dikes  and  veins  in  granites,  gneisses,  mica  schists,  and  crystalline  lime- 
stones. In  some  cases  it  is  the  result  of  metamorphic  action  on  carbo- 
naceous matter,  as  in  Rhode  Island,  or  it  may  be  due  to  the  reduction  of 
carburetted  vapors,  as  in  Ceylon,  or  of  the  oxides  of  carbon,  as  at  Ti- 
conderoga  and  vicinity  in  the  eastern  part  of  New  York  State.  Common 
associates  are  calcite,  orthoclase,  quartz,  pyroxene,  garnet,  spinel,  and 
amphibole.  The  principle  sources  are:  Ceylon;  Madagascar;  Chosen 
(Korea);  Sonora,  Mexico;  Austria;  eastern  New  York;  Chester  County, 
Pennsylvania;  Clay  County,  Alabama;  and  Dillon,  Montana. 

Artificial  graphite  is  now  manufactured  in  large  quantities  from 
anthracite  coal  or  petroleum  coke  in  the  electric  furnace  at  Niagara 
Falls,  New  York.  In  1913  over  6,800  tons  of  artificial  graphite  were 
produced. 

Graphite  is  used  extensively  in  the  manufacture  of  crucibles,  stove 
polish,  foundry  facings,  lead  pencils,  paint,  lubricants,  and  electrodes. 

SULPHUR  (Brimstone),  S. 

Orthorhombic,  bipyramidal  class.  Crystals  are  common,  showing 
mostly  pyramidal  or  tabular  habits,  Figs.  407  and  408.  Also  in  granular, 
fibrous,  earthy  powdery,  or  stalactitic  masses  (Fig.  409). 


FIG.  407. 


FIG.  408. — Sulphur  with  calcite. 
Racalmuto,  Sicily. 


FIG.  409. — Banded  sul- 
phur in  limestone.  Racal- 
muto, Sicily. 


Indistinct  cleavages.  Pronounced  conchoidal  to  uneven  fracture. 
Hardness  1.5  to  2.5.  Specific  gravity,  1.9  to  2.1.  Adamantine  luster 
on  crystal  faces,  otherwise  resinous  to  greasy.  Transparent  to  trans- 
lucent. White  to  yellow  streak.  Usually  sulphur  yellow  in  color; 
also  honey-yellow,  or  yellow  brown,  and  due  to  impurities,  red- 
dish, greenish,  or  grayish.  Non-conductor  of  electricity  and  heat. 
On  account  of  the  low  conductivity  and  unequal  distribution  of  heat,  cold 

13 


194  MINERALOGY 

crystals  often  crack  when  held  in  the  hand.     When  held  to  the  ear  a 
crackling  sound  may  be  heard. 

Usually  practically  pure  sulphur;  sometimes  mixed  with  bitumen  and 
clay.  Melts  at  114.5°  C.,  and  at  270°  C.  burns  with  a  bluish  flame  to 
sulphur  dioxide.  Insoluble  in  water  and  acids.  Soluble  in  carbon 
disulphide. 

The  large  and  commercially  important  deposits  occur  in  sedimentary 
rocks  and  are  generally  the  result  of  the  reduction  of  sulphate  minerals, 
notably  gypsum.  The  common  associates  are  celestite,  gypsum,  arago- 
nite,  and  calcite.  In  the  United  States,  important  producing  localities 
are  near  Lake  Charles  in  southwestern  Louisiana,  and  at  Freeport, 
Texas.  Here  by  means  of  superheated  water  and  compressed  air  the 
sulphur  is  pumped  to  the  surface  in  a  molten  condition,  and  allowed  to 
solidify  in  large  vats.  It  is  then  ready  for  shipment,  being  99.5  per  cent, 
pure  sulphur.  Girgenti,  Sicily,  has  for  many  years  been  the  chief  center 
of  the  sulphur  industry  of  Sicily.  Sulphur  is 
found  in  small  quantities  around  volcanoes,  the 
result  of  sublimation  or  interaction  of  sulphurous 
vapors;  thus,  on  Mounts  Vesuvius  and  ^Etna, 
also  in  Iceland,  Japan,  and  Hawaii.  It  occurs 
also  as  the  result  of  deposition  from  certain  hot 
springs,  and  from  the  decomposition  of  pyrite 
and  other  sulphide  minerals. 

Important   in  the   manufacture  of  sulphuric 
Fldretsbe7gfrGee±anyAn~    acid,    matches,    gunpowder,    vulcanized   rubber, 
insecticides,  medicines,  the  bleaching  of  silk,  straw, 

and  woolen  materials,  and  in  the  preparation  of  wood  pulp  used  in  the 
manufacture  of  paper. 

Semi -metals — Arsenic  Group 

The  members  of  this  group  crystallize  in  the  hexagonal  system  in 
pseudo-cubical  rhombohedrons.  They  are  brittle  and  non-malleable. 

Arsenic  (Native  Arsenic),  As. 

Hexagonal,  di trigonal  scalenohedral  class.  Crystals  are  pseudo- 
cubical  rhombohedrons,  but  very  rare.  Commonly  in  compact,  scaly, 
granular,  or  fine  grained  masses  with  reniform  and  botryoidal  structures 
(Fig.  410).  Often  breaks  into  concentric  or  onion-like  layers. 

.  Basal  cleavage,  but  usually  not  conspicuous.  Uneven  and  fine 
grained  fracture.  Hardness  3  to  4.  Specific  gravity  5.6  to  5.8.  Metallic 
luster.  Opaque.  Tin-white  color  on  fresh  fracture  surface,  tarnishes 
dark  gray  to  black  on  exposure.  Grayish  streak. 

Arsenic,  often  contains  antimony;  also  bismuth,  cobalt,  nickel, 
silver,  iron,  or  gold. 


DESCRIPTIVE  MINERALOGY 


195 


Found  principally  in  veins  with  silver,  cobalt,  and  nickel  ores;  thus 
in  the  Freiberg  mining  district  of  Saxony;  Joachimsthal,  Bohemia; 
Kongsberg,  Norway;  Mexico;  Chile. 

Native  arsenic  furnishes  but  a  small  portion  of  the  arsenic  used  in 
commerce  and  industry.  Artificial  metallic  arsenic  is  a  constituent  of 
shot  metal. 

Bismuth  (Native  Bismuth),  Bi. 

Hexagonal,  ditrigonal  scalenohedral  class.  Rarely  in  rhombohedral 
crystals.  Usually  in  compact,  reticulated,  arborescent,  platy,  or  compact 
masses  (Fig.  411). 

Basal  cleavage,  generally  conspicuous.  Hardness  2  to  2.5.  Specific 
gravity  9.7.  Brittle,  slightly  malleable  when  heated.  Metallic  luster. 
Opaque.  Reddish  white  color,  often  with  brassy  tarnish  colors.  Shiny 
lead  gray  streak. 


FIG.  411. — Bismuth  with  caleite  and  smaltite.     Cobalt,  Ontario. 

Bismuth,  often  with  traces  of  arsenic,  sulphur,  and  tellurium. 

Not  especially  abundant,  but  usually  in  veins  associated  with  silver, 
cobalt,  lead,  zinc,  and  tin  ores.  Important  localities  are:  Freiberg, 
Saxony;  Joachimsthal,  Bohemia;  Bolivia;  Cornwall,  England;  Cobalt, 
Ontario. 

Native  bismuth  is  a  source  of  the  metal  and  its  compounds.  The 
metal  is  used  in  the  manufacture  of  easily  fusible  alloys,  such  as  find 
application  in  automatic  sprinklers  and  safety  plugs  in  boilers;  also  in 
rifle  bullets  and  thermo  piles.  The  salts  of  bismuth  are  used  in  medicine, 
calico  printing,  and  in  the  manufacture  of  highly  refractive  glass. 

Metals^ 

Only  the  four  very  important  elements  platinum,  copper,  silver,  and 
gold  will  be  described. 

PLATINUM  (Native  Platinum),  Pt. 

Cubic,  hexoctahedral  class.  Small  crystals,  generally  cubes,  but 
very  rare.  Usually  in  scales  or  grains ;  also  in  nuggets. 


196  MINERALOGY 

Hackly  fracture.  Metallic  luster.  Opaque.  Hardness  4  to  6. 
Specific  gravity  14  to  19;  melted  platinum  is  19.7,  hammered  21.23. 
Malleable,  ductile,  sectile.  Silver  white  to  dark  gray  or  black  in  color. 
May  be  magnetic  if  much  iron  is  present. 

Platinum,  usually  contains  iron  (up  to  19.5  per  cent.),  and  smaller 
amounts  of  iridium,  rhodium,  palladium,  osmium,  copper,  and  at  times 
gold.  Infusible  at  ordinary  temperatures,  but  may  be  fused  and  welded 
with  the  oxyhydrogen  blowpipe.  Soluble  in  hot  concentrated  nitro- 
hydrochloric  acid. 

Platinum  was  first  discovered  in  1735  in  the  gold  placers  of  the  Pinto 
river  in  Colombia,  associated  with  gold,  zircon,  magnetite,  chromite  and 
so  forth.  In  1822  it  was  found  in  the  alluvial  deposits  of  Nizhni  Tagilsk 
in  the  Ural  Mountains.  Although  practically  all  of  the  world's  supply  is 
obtained  from  placer  deposits,  platinum  also  occurs  in  veins  associated 
with  chromite  and  disseminated  in  peridotite  rocks.  Russia  is  the  chief 
producer  and  controls  the  market.  In  the  United  States  small  amounts 
are  found  in  the  black  sands  of  the  rivers  along  the  Pacific  coast.  Impor- 
tant occurrences  in  veins  and  disseminated  have  been  recently  discovered 
near  Bunkerville,  Clark  County,  Nevada,  and  in  Westphalia,  Germany. 

Platinum  is  used  very  extensively  in  the  manufacture  of  sulphuric 
acid  (contact  method)  and  in  physical,  chemical,  and  electrical  apparatus ; 
also  in  jewelry,  pyrography,  dentistry,  non-magnetic  watches,  and  sur- 
gical instruments.  It  was  worth  $.35  a  gram  in  1895,  $.70  in  1901,  $1.10 
in  1910,  $1.50  in  1913,  $2.75  in  1916,  $5.55  in  1918,  and  $3.90,  July,  1920. 

Copper  Group 

The  very  important  metals  copper,  silver,  and  gold  belong  to  this 
group.  They  crystallize  in  the  cubic  system,  are  rather  soft,  heavy,  and 
very  malleable. 

COPPER  (Native  Copper),  Cu. 

Cubic,  hexoctahedral  class.  Crystals  are  rather  common,  but  usually 
distorted  and  in  parallel  groups.  Tetrahexahedrons,  rhombic  dodeca- 
hedron, and  cube  are  the  most  commonly  observed  forms  (Figs.  412, 
413,  and  414).  Generally  in  scales,  grains,  plates,  and  masses,  often- 
times weighing  many  tons;  less  frequently  arborescent  and  filiform. 

Hackly  fracture.  Hardness  2.5  to  3.  Specific  gravity  8.5  to  9. 
Metallic  luster.  Ductile  and  malleable.  Color  copper-red  on  fresh  frac- 
ture. Due  to  tarnish  and  decomposition  products,  color  may  be  super- 
ficially black  (CuO),  red  (Cu20),  green  (CuCO3.Cu(OH)2),  or  blue 
(2CuCO3.Cu(OH)2).  Streak  copper  red,- metallic  and  shiny.  Excellent 
conductor  of  heat  and  electricity. 

Generally  almost  pure  copper;  sometimes  contains  small  amounts  of 
silver  or  arsenic. 


DESCRIPTIVE  MINERALOGY 


197 


The  most  important  locality  for  the  occurrence  of  native  copper 
is  Keweenaw  Peninsula  in  Northern  Michigan,  where  it  occurs  dissemi- 
nated, principally  in  fine  grains  or  scales,  or  in  veins  in  (1)  dark  colored 


FIG.  412. — Crystallized  cop- 
per (tetrahexahedron) .  Phoenix 
Mine,  Lake  Superior  District. 


FIG.  413. — Crystallized  copper 
(rhombic  dodecahedron) .  Lake 
Superior  District. 


FIG.  414. — Crystallized  copper.     Lake  Superior  District. 

igneous  rocks,  called  melaphyr  amygdaloids  (Figs.  415  and  416),  (2)  in 
reddish  quartz  porphyry  conglomerates  (Fig.  417);  (3)  in  sandstones; 
(4)  in  epidotic  beds;  (5)  in  felsitic  rocks.  The  first  two  occurrences  are  at 


FIG.  415. — Copper  in  amygdaloid. 
Lake  Superior  District. 


FIG.  416. — "Shot"  copper.     Adventure 
Mine,  Lake  Superior  District. 


present  the  most  important.  These  ores  average  about  1  per  cent,  of 
copper  and  are  easy  to  treat.  By  means  of  crushing,  washing,  and 
concentrating  with  jigs  and  tables  the  metallic  copper  is  readily  extracted. 
It  is  then  smelted  and  refined,  and  cast  into  ingots  and  sold  as  "lake" 


198 


MINERALOGY 


copper.  In  1915  this  district  produced  241,951,921  pounds.  About 
80  per  cent,  of  the  ore  handled  was  amygdaloid  rock.  The  common  asso- 
ciates are  calcite,  quartz  .(Fig.  418),  datolite  (Fig.  419),  epidote,  silver, 
analcite,  and  other  zeolites. 


FIG.  417. — Copper  conglomerate.     Lake  Superior  District. 

Native  copper  also  occurs  in  smaller  quantities  associated  with  the 
other  copper  minerals — malachite,  azurite,  cuprite,  chalcopyrite,  bornite, 
and  chalcocite — especially  in  Arizona  and  New  Mexico. 

Metallic  copper  is  used  very  extensively  in  commerce  and  industry. 
Large  amounts  are  used  in  the  manufacture  of  copper  wire,  nails,  and 


FIG.  418. — Copper  with  cal- 
cite and  quartz.  Lake  Superior 
District. 


FIG.  419. — Copper  with  datolite  (white). 
Lake  Superior  District. 


sheets,  brass,  bronze,  electrical  apparatus,  munitions  of  war;  also  for 
coinage  purposes  and  chemical  reagents.  It  is  said  that  there  are  about 
600  uses  for  copper  where  it  is  practically  indispensable.  The  price  of 
metallic  copper  fluctuates  greatly,  in  1912  it  averaged  about  16  cents 
a  pound,  in  1913  about  15  cents,  in  1914  about  13  cents,  in  1915  about 
17.25  cents,  in  1918  about  25  cents,  and  in  July,  1920  about  19  cents. 


DESCRIPTIVE  MINERALOGY 


199 


SILVER  (Native  Silver),  Ag. 

Cubic,  hexoctahedral  class.  Crystals  usually  small  and  distorted, 
and  in  parallel  groups.  Cubes  and  octahedrons  most  common.  Also 
acicular,  reticulated,  or  arborescent;  fine  threads  or  wires  (Figs.  420 
and  421),  sometimes  matted  and  resembling  tufts  or  wads  of  hair;  scales, 
plates,  or  large  masses. 


FIG.  420. — "Wire"  silver  with  argentite. 
Bolivia. 


Porco, 


FIG.  421.— "Wire"  sil- 
ver. Cliff  Mine,  Lake 
Superior  District. 


Malleable  and  ductile.  Hardness  2.5  to  3.  Specific  gravity  10  to  12. 
Metallic  luster.  Color  silver  white,  usually  with  yellow  brown,  gray,  or 
black  tarnish  colors.  Silver  white  streak,  shiny.  Excellent  conductor  of 
heat  and  electricity. 


FIG.  422.— Silver  (white) 
and  copper  "Half  Breed." 
Lake  Superior  District. 


FIG.  423. — Silver  with  calcite.     La- 
Rose  Mine,  Cobalt,  Ontario. 


Silver,  often  with  varying  amounts  of  gold,  up  to  28  per  cent.;  also 
with  copper,  arsenic,  antimony,  mercury,  iron,  and  platinum. 

Occurs  commonly  with  ores  of  silver,  lead,  copper,  arsenic,  cobalt 
and  nickel,  associated  with  calcite,  quartz,  barite,  or  fluorite.  Kongsberg, 


200  MINERALOGY 

Norway,  has  furnished  a  great  deal  of  silver  in  the  form  of  crystals  and 
large  masses,  some  weighing  750  pounds.  The  Saxon  mines  at  Freiberg, 
Marienberg,  and  Annaberg  have  long  been  heavy  producers;  also  Mexico, 
especially  Sonora,  Durango,  Sinaloa;  Chile;  Peru;  and  Bolivia  Several 
of  the  more  important  localities  in  the  United  States  are :  Bingham  and 
Tintic  districts,  Utah;  Butte,  Montana  (from  copper  ores);  Tonopah, 
Nevada;  Coeur  d'Alene,  Idaho;  Aspen,  Colorado;  Lake  Superior  copper 
district,  associated  with  copper,  forming  "  half-breeds "  (Fig.  422).  In 
large  deposits,  disseminated  and  in  veins,  at  Cobalt,  Ontario,  associated 
with  niccolite,  smaltite,  erythrite,  annabergite,  bismuth,  and  calcite  (Fig. 
423).  Many  masses  from  this  locality  were  95  per  cent,  silver  and 
weighed  from  600  to  1,000  pounds.  Rarely  found  as  nuggets. 

Native  silver  is  used  for  coinage,  jewelry,  and  ornamental  purposes; 
also  in  physical,  chemical,  and  surgical  apparatus.  The  price  varies 
greatly,  and  is,  July,  1920,  about  $1.00  an  ounce. 

GOLD  (Native  Gold),  Au. 

Cubic,  hexoctahedral  class.  Crystals  are  small,  more  or  less  dis- 
torted, but  only  rarely  found.  The  most  common  forms  are  the  octa- 
hedron, cube,  and  rhombic  dodecahedron,  oc- 
curring either  independently  or  in  combina- 
tion. Skeletal  development  frequent.  Usu- 
ally in  disseminated  or  rolled  scales  or  grains; 
also  filiform,  recticulated,  and  in  large  lumps 
or  nuggets  (Fig.  424). 

Malleable  and  ductile.  No  cleavage, 
hackly  fracture.  Hardness  2.5  to  3.  Specific 
gravity  15.6  to  19.3.  Metallic  luster.  Go'den 
to  brassy  or  light  yellow  in  color  depending 
upon  the  amount  of  silver  present.  Opaque. 

FIG.    424. — Gold  in  conglomer-  „.    ,  ,        .  , 

ate.  Western  Sonora,  Mexico.  Gold,  with  varying  amounts  of  silver  (up 

to  40  per  cent.) ;  also  iron,  copper,  bismuth, 

and  so  forth.  Readily  fusible  and  soluble  in  nitro-hydrochloric  acid. 
Readily  acted  upon  by  chlorine,  and  potassium  or  sodium  cyanide. 
Forms  an  amalgam  with  mercury. 

Gold  occurs  widely  distributed,  but  in  only  a  comparatively  few 
places  in  sufficient  quantities  to  be  of  economic  importance.  There  are 
two  general  types  of  occurrence,  namely:  (1)  in  situ,  and  (2)  in  secondary 
deposits,  called  placers. 

Gold  occurring  in  situ  is  usually  found  disseminated  in  quartz  veins, 
and  associated  with  various  sulphide  minerals,  of  which  pyrite  is  the 
most  important.  Owing  to  the  decomposition  of  the  associated  sulphides, 
the  quartz,  where  exposed  on  the  surface  to  the  action  of  percolating 
water — zone  of  oxidation — is  usually  more  or  less  cellular  and  of  a  rusty 


DESCRIPTIVE  MINERALOGY 


201 


appearance.  Such  quartz  is  often  called  "porous"  or  "rusty"  quartz. 
Gold  is  also  found  disseminated  in  granites,  trachytes,  andesites,  crystal- 
line schists,  sandstones,  and  conglomerates.  The  most  common  as- 
sociates, aside  from  quartz  and  pyrite,  are  chalcopyrite,  galena,  stibnite, 
tetrahedrite,  sphalerite,  and  arsenopyrite,  some  of  which  are  frequently 
auriferous  (Figs.  425  and  426). 

Free  milling  gold  is  usually  present  in  distinctly  visible  particles  and 
is  easily  recovered  by  crushing  and  washing  in  a  stamp  mill  and  sub- 
sequent amalgamation  with  mercury,  the  finely  crushed  material  from  the 
mill  being  allowed  to  flow  over  copper  plates  coated  with  mercury. 
Where  the  gold  is  associated  with  considerable  quantities  of  the  sulphides, 
the  chlorination  or  cyanide  processes  are  used,  either  alone  or  in  con- 
nection with  amalgamation.  In  the  chlorination  process  the  auriferous 
ores  are  roasted  and  then  subjected  to  the  action  of  chlorine  which  causes 


FIG.  425. — Gold  in  quartz.     Tuo- 
lumne  County,  California. 


FIG.  426. — Gold  bearing  con- 
glomerate. Rand  Mines,  Trans- 
vaal. 


the  gold  to  pass  into  solution.  In  the  cyanide  process  the  crushed  ores, 
either  raw  or  roasted,  are  treated  with  solutions  of  potassium  or  sodium 
cyanide,  whereby  a  soluble  double  cyanide  is  formed.  By  means  of 
electrolysis  the  gold  is  generally  separated  from  these  solutions.  These 
processes  permit  ores  carrying  very  small  amounts  of  gold,  sometimes 
as  low  as  SI. 50  per  ton,  to  be  worked  with  a  profit. 

Important  localities  for  the  occurrence  of  gold  in  situ  are:  California, 
Nevada,  South  Dakota,  Utah,  Alaska;  the  Rand  in  the  Transvaal,  South 
Africa;  Western  Australia,  New  South  Wales,  Ural  Mountains;  Porcu- 
pine district,  Ontario. 

Placer  gold  is  the  result  of  the  disintegration  of  rocks  containing  gold 
in  situ,  that  is,  disseminated  or  in  veins.  As  these  rocks  are  reduced  by 
the  action  of  the  atmospheric  agencies  and  erosion  to  sand  and  gravel, 


202  MINERALOGY 

the  gold,  on  account  of  its  very  high  specific  gravity,  becomes  concentra- 
ted in  the  stream  beds  in  auriferous  regions,  and  is  found  as  scales,  grains, 
and  nuggets.  Especially  rich  deposits  are  likely  to  be  found  where  the 
velocity  of  the  stream  has  been  checked  by  a  bend  in  its  course  or  by 
some  obstruction.  Placer  gold  is  readily  recovered  by  washing,  the  sand 
and  gravel  being  thrown  into  long  wooden  troughs  called  sluices. 
Through  these  sluices  water  flows  at  a  rather  rapid  rate  in  order  to  carry 
away  the  lighter  rock  material.  At  regular  intervals  cross-bars,  called 
riffles,  are  placed  in  the  trough  to  check  the  velocity  of  the  water.  This 
causes  the  heavy  particles  to  fall  to  the  bottom  of  the  sluices,  and  since 
mercury  is  added  from  time  to  time  and  is  also  caught  by  the  riffles, 
an  amalgam  of  gold  is  formed.  From  this  amalgam  the  gold  is  easily 
recovered  by  volatilizing  the  mercury.  In  some  localities  hydraulic 
mining  is  employed  in  working  placer  deposits.  This  does  not  differ 
essentially  from  the  above  method  and  consists  in  directing  a  large 
stream  of  water  under  high  pressure  against  the  bank  of  the  placer  in 
order  to  loosen  the  same  and  wash  the  sand  and  gravel  down  into  the 
sluices.  This  type  of  working  placers  is  practicable  only  where  there  is 
an  abundant  water-supply.  In  regions  where  the  supply  of  water  is 
limited,  dredges  are  used  to  advantage. 

Gold  placers  are  common  in  California,  Alaska,  Colorado,  Australia, 
and  Siberia.  In  practically  all  noteworthy  gold  producing  districts, 
gold  has  usually  been  found  first  in  placers,  and  by  subsequent  exploration 
the  primary  occurrences  in  situ  have  been  located. 

Gold  is  used  chiefly  for  coinage  and  jewelry.  Gold  coins  of  the  United 
States  consist  of  nine  parts  of  gold  and  one  of  copper.  For  jewelry 
purposes  copper  and  silver  are  alloyed  with  gold  to  increase  its  hardness. 
The  gold  content  of  such  alloys  is  expressed  in  carats,  thus  14  carat  gold 
consists  of  1^4ths  gold  and  ^^ths  other  metals. 


2.  SULPHIDES,  ARSENIDES,  AND  SULPHO-MINERALS 

This  group,  consisting  of  twenty-three  members,  includes  some  of  the 
most  important  ore  minerals. 

(a)  Sulphides  and  Arsenides 

REALGAR  AsS  Monoclinic 

ORPIMENT  As2S3  Monoclinic 

STIBNITE  Sb2S3  Orthorhombic 

Molybdenite  MoS2  Hexagonal 

SPHALERITE-PYRRHOTITE    GROUPS 

SPHALERITE  ZnS  Cubic 

PYRRHOTITE  FeS  Hexagonal 

Niccolite  NiAs  Hexagonal 


DESCRIPTIVE  MINERALOGY 


203 


PYRITE-MARCASITE  GROUPS 

PYRITE  FeS2 

Cobaltite  CoAsS 

Smaltite  CoAs2 

MARCASITE  FeS2 

ARSENOPYRITE  FeAsS 

GALENA-CHALCOCITE  GROUPS 

GALENA  PbS 

Argentite  Ag2S 

CHALCOCITE  Cu2S 


CINNABAR 


HgS 
(6)  Sulpho-minerals 


(a)  General  Formula, 

CHALCOPYRITE 
BORNITE 

Proustite 
Pyrargyrite 
Bournonite 
TETRAHEDRITE 


f  +  3 
Cu2Fe2S4 


Ag6As2S6 
AgeSboSe 
Pb2Cu2Sb2S6 

Ml?'"  Q 
8-Ix       2O7 


(6)  General  Formula,  M'XR?S  x 


Cu6AS2S8 


Cubic 
Cubic 
Cubic 

Orthorhombic 
Orthorhombic 


Cubic 

Cubic 

Orthorhombic 

Hexagonal 


Tetragonal 
Cubic 

Hexagonal 

Hexagonal 

Orthorhombic 

Cubic 


Orthorhombic 


Enargite 

.These  minerals  generally  possess  a  metallic  luster,  and  are  opaque 
and  heavv. 

a.  Sulphides  and  Arsenides 

Only  the  important  simple  sulphides  and  arsenides  will  be  described. 

REALGAR,  AsS. 

Monoclinic,  prismatic  class.  Crystals  are  usually  short  prismatic. 
Occurs  also  in  granular  and  compact  masses  and  as  incrustations  and 
coatings. 

Cleavages  parallel  to  clinopinacoid  and  orthoprism.  Conchoidal 
fracture.  Hardness  1.5  to  2.  Specific  gravity  3.5.  Resinous  luster. 
Aurora-red  to  orange  yellow  color.  Orange-yellow  streak.  Transparent 
to  translucent. 

AsS,  sometimes  written  As2S2.     Alters  to  orpiment. 

Occurs  with  ores  of  silver  and  antimony,  and  is  usually  associated 
with  orpiment.  Frequently  disseminated  in  clay  or  dolomite;  also  as  a 
sublimation  product  and  as  a  deposit  from  hot  springs. 

Some  notable  localities  are:  Kapnik  and  Felsobanya,  Hungary; 
Joachimsthal,  Bohemia;  Allcahr,  Macedonia;  Binnenthal,  Switzerland; 


204 


MINERALOGY 


Mount  Vesuvius;  Iron  County,  Utah;  Yellowstone  Park;  San  Bernar- 
dino and  Trinity  Counties,  California. 

This  mineral  is  usually  found  well  represented  by  beautiful  speci- 
mens in  mineral  collections,  but  is  of  no  economic  importance.  The  arti- 
ficial compound  is  used  in  the  manufacture  of  fire  works  and  pigments. 

ORPIMENT  (Auripigment,  Arsenical  Gold  Ore),  As2S3. 

Monoclinic,  prismatic  class.  Crystals  are  short  prismatic,  but  not 
common.  Usually  in  foliated  or  granular  masses,  sometimes  as  crusts. 

Cleavage  parallel  to  clinopinacoid.  Flexible  but  not  elastic.  Hard- 
ness 1.5  to  2.  Specific  gravity  3.5.  Resinous  to  pearly  luster.  Lemon 
yellow  color  and  streak.  Translucent  to  opaque.  Very  much  like 
realgar,  but  differs  in  color. 

As2S3,  often  formed  from  realgar,  with  which  it  is  commonly  associated. 

Formation  and  occurrence  are  the  same  as  for  realgar. 

Excellent  specimens  are  rather  common,  but  the  mineral  is  not  im- 
portant commercially.  The  artificial  compound  is  used  as  a  pigment, 
and  in  dyeing  and  tanning. 

STIBNITE  (Antimonite,  Gray  Antimony),  Sb2S3. 

Orthorhombic,  bipyramidal  class.  Crystals  common,  prismatic 
and  highly  modified  (Fig.  427),  often  vertically  striated,  bent,  or  twisted; 


FIG.  427. — Stibnite.     Province  of  lyo,  Island  of 
Shikoku,  Japan. 


FIG.  428. — Bladed  stibnite 
with  quartz.     Portugal. 


also  in  radial  aggregates;  bladed  (Fig.  428),  columnar,  granular,  and 
compact  masses. 

Cleavage  parallel  to  brachypinacoid.  Slightly  sectile.  Metallic 
luster.  Hardness  2.  Specific  gravity  4.65.  Lead  gray  in  color  and 
streak.  Often  tarnishes  black. 

Sb2S3,  sometimes  contains  gold  and  silver.  Fuses  easily  in  candle 
flame. 

Found  in  veins  with  quartz  and  various  antimony  minerals  resulting 
from  the  decomposition  of  stibnite.  Also  with  galena,  barite,  cinnabar, 
sphalerite,  and  gold.  Occurs  in  Saxony,  Bohemia,  Siberia,  Algeria, 


DESCRIPTIVE  MINERALOGY  205 

Mexico,  and  China.  Excellent  crystals  have  been  obtained  from  Shi- 
koku,  Japan.  The  chief  American  localities  are:  Idaho,  Nevada,  Utah, 
Alaska,  California;  also  Washington  and  Arkansas. 

Stibnite  is  the  chief  source  of  metallic  antimony  and  its  compounds. 
It  is  used  in  fireworks,  safety  matches,  rubber  goods,  and  percussion  caps. 

Bismuthinite,  Bi2S3,  resembles  stibnite  very  closely.     Not  common. 

MOLYBDENITE,  MoS2. 

Hexagonal,  dihexagonal  bipyramidal  class.  Rarely  in  tabular 
or  prismatic  hexagonal  crystals  (Fig.  429).  Generally  in  disseminated 
scales  or  grains;  sometimes  in  foliated  or  granular  masses. 

Excellent  basal  cleavage.  Flexible.  Greasy  feel.  Marks  paper. 
Blue  gray  in  color  (graphite  is  black).  Hardness  1  to  1.5.  Specific 

gravity  4.75  (graphite  1.9  to  2.3).     Greenish  streak    

on  glazed  porcelain  (graphite  shiny  black). 

MoS2,  sometimes  contains  gold  or  silver. 

Generally   disseminated   in   granites,    especially 
those  associated  with  tin  ore  deposits;  also  in  sye- 
nites,  gneisses,   and   crystalline  limestones.     Com- 
monly with  cassiterite,  wolframite,  topaz,  epidote, 
and  chalcopyrite.    Large  crystals  occur  in  Renfrew 
County,  Ontario.     Important  occurrences  in  Saxony        FIG.  429.— Moiyb- 
and  Bohemia;  Cornwall,  England;  Queensland  and    J^t^  Wake  fie  id, 
New    South    Wales,    Australia;  Cooper   and   Blue 
Hill,   Maine;  Westmoreland,  New  Hampshire;   Crown  Point,   Chelan 
County,  Washington;  Pitkin,  Colorado. 

Chief  source  of  molybdenum  and  its  compounds.  Used  in  the 
manufacture  of  molybdenum  "high  speed"  steels. 

Sphalerite  -pyrrhotite  Groups 

These  groups  form  an  important  isodimorphous  series,  sphalerite 
and  related  minerals  crystallizing  in  the  cubic  system,  while  the  members 
of  the  pyrrhotite  group  belong  to  the  hexagonal  system. 

SPHALERITE  (Blende,  Zinc  Blende,  Black  Jack),  ZnS. 

Cubic,  hextetrahedral  class.  Crystals  are  common;  often  highly 
modified,  and  distorted  or  rounded  (Fig.  433).  Tetrahedrons  with  cube 
or  rhombic  dodecahedron  are  most  commonly  observed  (Figs.  430  and 
431).  Twins  according  to  the  Spinel  law.  Generally  incleavable, 
fine  to  coarse  granular,  and  compact  masses;  also  fibrous  and  botryoidal. 

Highly  perfect  rhombic  dodecahedral  cleavage  (Fig.  432).  Brittle. 
Resinous  to  adamantine  luster.  Hardness  3.5  to  4.  Specific  gravity 
3.9  to  4.2.  Color  varies  greatly;  when  pure,  white;  commonly,  yellow, 
red,  black,  or  green.  Transparent  to  translucent.  Streak  white,  pale 


206 


MINERALOGY 


yellow,    or   brown.     Sometimes    phosphoresces    when    broken,    rubbed, 
or  scratched  (Triboluminescence) . 


FIG.  430. 


FIG.  431. 


FIG.  432. — Sphalerite.  Cleavage 
rhombic  dodecahedron.  Jo  pi  in, 
Missouri. 


FIG.  433. — Sphalerite.     Joplin,  Missouri.  FIG.    434. — Sphalerite    with 

quartz      and      galena,      Kapnik, 
Hungary. 


FIG.    435. — Sphalerite    in  chert. 
Galena,  Illinois. 


FIG.  436. — Sphalerite  with 
galena  and  calcite.  Webb  City, 
Missouri. 


ZnS,   usually  contains  iron,   up    to    18    per  cent.,   also  manganese, 
cadmium,  or  mercury. 


DESCRIPTIVE  MINERALOGY 


207 


Occurs  extensively  in  dolomitic  limestones  and  other  sedimentary 
rocks,  as  also  in  crystalline  rocks.  Usually  associated  with  galena, 
chalcopyrite,  pyrite,  barite,  fluorite,  siderite,  rhodochrosite,  and  quartz 
(Figs.  434,  435,  and  436).  Commonly  in  veins  and  cavities;  also  in 
extensive  deposits.  Important  localities  are:  Freiberg,  Saxony;  Pribram, 
Bohemia;  Binnenthal,  Switzerland;  Cornwall,  England;  and  Yechigo, 
Japan. 

In  the  United  States,  sphalerite  is  very  common  in  the  limestones  of 
Missouri,  Kansas,  Oklahoma,  Wisconsin,  Arkansas,  Iowa,  and  Illinois; 
beautiful  crystals  at  Joplin,  Missouri.  Also  found  with  lead  and  silver 
ores  in  the  western  states.  Found  in  many  places  in  smaller  quantities. 

Sphalerite  is  the  chief  source  of  zinc.  Metallic  zinc,  known  com- 
mercially as  spelter,  is  used  in  large  quantities  in  galvanizing  iron  and  in 
the  manufacture  of  brass,  zinc  wire  and  sheets,  shot,  dust  zinc,  electric 
batteries.  The  various  compounds  of  zinc  are  employed  extensively 
as  pigments,  in  chemistry  and  medicine. 

The  following  three  minerals  belong  to  the  sphalerite  group  but  are  not  common: 
Alabandite,  MnS;  Pentlandite  (Fe,  Ni)S;  Troilite,  FeS. 

PYRRHOTITE  (Magnetic  Pyrites),  FeS. 

Hexagonal,  ditrigonal  pyramidal  class.  Crystals  are  tabular  or 
pyramidal  (Fig.  437),  but  not  common.  Usually  massive,  granular  or 
lamellar. 


FIG.  437. — Pyrrhotite  with  sphalerite.     Near  El  Paso,  Texas. 

Inferior  basal  cleavage.  Brittle.  Hardness  3.5  to  4.  Specific 
gravity  4.5  to  4.6.  Metallic  luster.  Opaque.  Bronze  yellow  to  bronze 
red  in  color,  tarnishing  easily  to  dark  brown.  Streak  grayish  black. 
Powder  frequently  attracted  by  the  magnet. 

FeS,  with  up  to  6  per  cent,  of  sulphur  in  solid  solution.  Often  con- 
tains nickel  and  cobalt. 

Usually  as  a  magmatic  segregation  in  basic  igneous  rocks  such  as 
gabbros,  norites,  and  peridotites,  and  commonly  associated  with  pyrite, 
chalcopyrite,  pentlandite,  and  galena.  Important  localities  are:  Kongs- 
berg,  Norway;  Bodenmais,  Bavaria;  Sudbury,  Canada;  Stafford  and  Ely, 


208 


MINERALOGY 


Vermont;     Ducktown,     Tennessee;     Gap     Mine,     Lancaster     County, 
Pennsylvania. 

An  important  source  of  nickel  and  cobalt. 


Crystals  are  rare.     Nearly 


Metal- 


NICCOLITE  (Copper  Nickel),  NiAs. 

Hexagonal,  ditrigonal  pyramidal  class, 
always  massive  or  disseminated  (Fig.  438). 

Uneven  fracture.  Hardness  5.5.  Specific  gravity  7.3  to  7.7. 
lie  luster.  Light  copper  red  in  color,  tarnishes  brown  or  grayish.  Often 
coated  with  a  green  crust  of  annabergite,  Ni3As208.8H2O.  Streak 
brownish  black. 

NiAs,  with  small  amounts  of  iron,  cobalt,  antimony,  and  sulphur. 

Commonly  associated  with  nickel,  cobalt,  and 
silver  ores,  thus  in  the  Freiberg  district  of  Sax- 
ony; Joachimsthal,  Bohemia;  the  Cobalt  district 
of  Ontario;  in  smaller  quantities  at  Franklin 
Furnace,  New  Jersey;  Silver  Cliff,  Colorado. 
A  nickel  ore. 

Other  members  of  the  pyrrhotite  group  are  Wurt- 
zite,  ZnS;  Greenockite,  CdS;  Millerite,  NiS;  Breithaup- 
tite,  NiSb. 

Pyrite-marcaslte   Groups 


FIG.  438.— Niccolite. 
Cobalt,  Ontario. 


These  minerals  form  an  interesting  iso- 
dimorphous  series,  pyrite,  cobaltite,  and  smal- 
tite  crystallizing  in  the  cubic  system,  while  marcasite  and  arsenopyrite 
possess  the  symmetry  of  the  orthorhombic  bipyramidal  class. 

PYRITE  (Fool1 8  Gold,  Iron  Pyrites) ,  FeS2. 

Cubic,  dyakisdodecahedral  class.  Crystals  are  common,  often  large. 
The  common  forms  are  the  cube,  octahedron,  and  pyritohedron  (Figs.  439 
and  440) ;  frequently  distorted  and  highly  modified.  Crystal  faces,  especi- 
ally those  of  the  cube,  often  show  striatlons  conforming  to  the  symmetry 
of  the  dyakisdodecahedral  class  (Fig.  442).  Penetration  twins  of  pyrito- 
hedrons  with  the  twinning  plane  parallel  to  a  face  of  the  rhombic  dode- 
cahedron (Fig.  441),  are  sometimes  called  crystals  of  the  "iron  cross." 
Also  massive  and  disseminated  granular,  reniform,  botryoidal,  stalactitic. 

Uneven  fracture.  Hardness  6  to  6.5.  Specific  gravity  4.9  to  5.2. 
Brittle.  Metallic  luster.  Opaque.  Pale  brassy  to  golden  yellow  in 
color,  sometimes  with  brown  or  variegated  tarnish  colors.  Greenish  to 
brownish  black  streak. 

FeS2,  with  cobalt,  nickel,  copper,  arsenic,  and  gold  in  varying  amounts. 
Decomposes  readily,  especially  in  a  moist  atmosphere.  Limonite  and 
goethite  are  the  usual  decomposition  products,  although  various  sul- 


DESCRIPTIVE  MINERALOGY 


209 


phates  and  sulphuric  acid  sometimes  result.     Pseudomorphs  of  limonite 
after  pyrite  are  quite  common  (Fig.  443). 

Pyrite  is  the  most  common  sulphide  mineral  and  hence  is  found  very 
widely  distributed.     It  occurs  in  rocks  of  all  ages.     Its  mode  of  occur- 


4 


© 


FIG.  439. — Pyrite  crystals — octahedron,  striated  cube,  cube 
and  octahedron,  pyritohedron. 


FIG.  441. 


FIG.  440. — Pyrite.     Bingham 
Canyon,   Utah. 


FIG.  442. — Pyrite.     Striated  cubes. 
Leadville,  Colorado.  / 


FIG.  443. — Limonite  pseudomorphs  after  pyrite.     Hartz  Mountains,  Germany. 

rence  varies  greatly.  Usually  associated  with  other  sulphides,  such  as 
galena,  chalcopyrite,  sphalerite,  and  arsenopyrite;  also  with  calcite, 
siderite,  hematite,  and  magnetite.  Commonly  found  in  quartz  with 
native  gold.  As  nodules  and  concretions  in  many  slates,  sandstones,  and 
coals. 

14 


210  MINERALOGY 

Excellent  crystals  are  found  in  the  Freiberg  district,  Saxony;  Pribram, 
Bohemia;  Schemnitz,  Hungary;  enormous  deposits  carrying  gold  and 
silver  at  Rio  Tinto,  Spain.  In  the  United  States,  especially  good  crystals 
occur  at  Franklin  Furnace,  New  Jersey;  Central  City  Mine,  Gilpin 
County,  and  elsewhere  in  Colorado;  French  Creek,  Pennsylvania.  Large 
deposits  of  massive  pyrite  occur  in  Virginia,  New  York,  California, 
Massachusetts,  and  Georgia. 

Pyrite  is  used  principally  as  a  source  of  sulphur  dioxide  in  the  manu- 
facture of  sulphuric  acid,  and  of  sulphate  of  iron,  known  as  copperas. 
Pyrite  is  also  a  source  of  gold  and  copper.  Small  quantities  are  used  as 
detectors  in  wireless  apparatus. 

COBALTITE    (Cobalt  Glance),   CoAsS. 

Cubic,  dyakisdodecahedral  class.  Usually  as  small,  well  developed 
crystals  showing  either  the  cube  or  pyritohedron.  Sometimes  both  in 
combination.  Cube  faces  striated  as  shown  in  Fig.  442,  page  209. 
More  rarely  compact  and  granular. 

Cubical  cleavage.  Uneven  fracture.  Brittle.  Hardness  5.5.  Spe- 
cific gravity  6  to  6.4.  Metallic  luster.  Opaque.  Silver  white  color,  at 
times  with  a  reddish  tinge;  grayish  if  much  iron  is  present.  Often  with  a 
pink  coating  of  erythrite,  Co3As.2O8.8H2O.  Grayish  black  streak. 

CoAsS,  usually  with  iron  up  to  12  per  cent. 

Generally  in  small  quantities  with  other  cobalt  minerals;  also  with 
pyrrhotite,  chalcopyrite,  pyrite,  galena,  magnetite.  Occurs  at  Tunaberg, 
Sweden;  Skutterud  and  Nordmark,  Norway;  Cornwall,  England;  Cobalt 
district,  Ontario. 

A  source  of  cobalt. 

SMALTITE,CoAs2. 

Cubic,  dyakisdodecahedral  class.  Crystals  generally  cubic  in  habit 
but  rare.  Usually  massive, — compact,  granular,  lamellar,  or  fibrous. 

Uneven  fracture.  Brittle.  Hardness  5.5.  Specific  gravity  6.4  to  6.6. 
Metallic  luster.  Opaque.  Tin  white  to  light  steel  gray  in  color.  Tarn- 
ishes dull.  Often  coated  with  erythrite,  CosAs2O8.8H2O.  Grayish 
black  streak.  Garlic  odor  when  struck  with  a  hammer.  Difficult  to 
distinguish  by  physical  properties  from  chloanthite,  NiAs2. 

CoAs2,  usually  with  varying  amounts  of  nickel,  iron,  and  sulphur. 
Iron  may  amount  to  18  per  cent.,  causing  higher  specific  gravity. 

Most  common  cobalt  mineral;  usually  with  cobalt,  nickel,  and  silver 
ores;  also  native  bismuth,  barite,  siderite,  quartz,  arsenopyrite.  Thus,  in 
the  Freiberg  district,  Saxony;  Cornwall,  England;  Tunaberg  Sweden; 
La  Motte  mine,  Missouri;  Cobalt  district,  Ontario.  *  ; 

An  important  source  of  cobalt. 

Other  members  of  the  pyrite  group  are  Hauerite,  MnS_>;  Gersdorffite,  NiAsS; 
Ullmannite,  NiSbS;  Chloanthite,  NiAs2;  Sperrylite,  PtAs2. 


DESCRIPTIVE  MINERALOGY 


211 


MARCASITE   (White  Iron   Pyrites,  Spear   Pyrites),    FeS2. 

Orthorhombic,  bipyramidal  class.  Crystals  usually  tabular  or 
short  columnar;  elongated  and  striated  parallel  to  a  axis.  Often  twinned 
resembling  cock's  combs  or  spear  heads  (Figs.  444  and  445).  Com- 
monly massive  fine  granular,  stalactitic,  reniform,  and  globular;  often 
with  radial  structures. 

Hardness  6  to  6.5.  Specific  gravity  4.6  to  4.8.  Metallic  luster. 
Pale  brass  yellow  to  steel  gray  in  color,  darker  after  exposure.  Usually 
lighter  in  color  than  pyrite.  Streak  greenish  black. 

FeS2,  contains  at  times  arsenic  and  copper.     Alters  more  readily  than 
pyrite  forming  limonite  and  melanterite. 
Powdered  marcasite  dissolves  in  concen- 
trated   nitric    acid    with   separation   of 
sulphur,  while  pyrite  does  not. 


FIG.  444. — Marcasite.     Ossegg,  Bohemia. 


FIG.  445. — Marcasite.     Ossegg, 
Bohemia. 


Not  as  abundant  as  pyrite.     When  massive  difficult  to  distinguish 
from  pyrite.     Frequently  with  pyrite,  galena,  calcite,  fluorite,  and  sphal- 
erite.    Common  as  concretions  in  marl,  clay,  limestone,  and  coal.     In 
chalk  marl  at  Folkestone,  England;  Bohe- 
mia; Saxony;  with  sphalerite,  galena,  and 
calcite  at  Joplin,  Missouri;    Mineral   Point, 
Wisconsin;  Galena,  Illinois. 

Uses  same  as  for  pyrite. 

Arsenopyrite  (Mispickel),  FeAsS. 

Orthorhombic,  bipyramidal  class.     Often 

in  disseminated,  tabular  or  short  prismatic 
crystals  (Fig.  446). 
Striated  parallel  to  the 
a  axis  (Fig.  447) .  Some- 
times twinned.  More 
generally  massive, — com- 

FIG.  446. 


FIG.  447. — Arsenopyrite  with 
quartz    and    galena.      Freiberg, 


pact,     granular,     COlum-     Germany. 

nar,  or  radial. 

Hardness  5.5.  to  6.     Specific  gravity  5.9  to  6.2.   Color  silver  white 


212  MINERALOGY 

to  light  steel  gray,  tarnishing  brass  yellow  or  gray.  Streak  black. 
Metallic  luster. 

FeAsS,  often  contains  cobalt,  antimony,  bismuth,  gold,  and  silver. 

Commonly  with  ores  of  tin,  nickel,  cobalt,  silver,  gold,  and  lead; 
also  with  pyrite,  chalcopyrite,  and  sphalerite.  Found  at  Freiberg, 
Saxony;  in  serpentine  at  Reichenstein,  Silesia;  Cornwall,  England; 
Tunaberg,  Sweden;  in  dolomite  in  Binnenthal,  Switzerland;  in  gold 
bearing  quartz  veins  at  Deloro,  Ontario;  Franconia,  New  Hampshire; 
Floyd  and  Montgomery  counties,  Virginia;  Washington. 

Used  principally  as  a  source  of  white  arsenic  or  arsenious  oxide,  the 
arsenic  of  commerce.  If  present  in  paying  quantities,  gold,  silver,  and 
cobalt  are  recovered. 

Other    members    of    the    marcasite    group   are  Lollingite,   FeAs2;    Glaucodote, 
(Co,Fe)AsS;  Safflorite,  CoAs2;  Wolfachite,  Ni(As,  S,  Sb)2;  Rammelsbergite,  NiAs2. 

Galena-chalcocite  Groups 

These  groups  form  an  isodimorphous  series.  The  members  of  the 
galena  group,  of  which  only  galena  and  argentite  will  be  described, 
crystallize  in  the  cubic  system.  Chalcocite  and  related  minerals  are 
orthorhombic  in  development.  Of  the  orthorhombic  group,  only  chalco- 
cite  is  of  suffiicent  importance  to  warrant  a  description. 

GALENA  (Galenite,  Lead  Glance),  PbS. 

Cubic,  hexoctahedral  class.  Well  developed  crystals  are  common. 
Usual  forms  are  the  cube  (h),  and  octahedron  (o),  independently  or  in 


FIG.  448.  FIG.  449.  FIG.  450.         FIG.  451.— Galena.     Joplin, 

Missouri. 

combination,  also  the  rhombic  dodecahedron  (d),  (Figs.  448,  449,  450, 
and  451).  Most  generally  in  cleavable  masses;  also  compact,  coarse  to 
fine  granular,  more  rarely  stalactitic  or  fibrous. 

Perfect  cubical  cleavage  (Fig.  452).  Hardness  2.5.  Specific  gravity 
7.3  to  7.6.  Metallic  luster,  especially  on  cleavage  surfaces  (Fig.  453); 
otherwise  rather  dull.  Lead  gray  color.  Grayish  black  streak. 

PbS,  often  with  small  amounts  of  silver.     On  this  account  galena 


DESCRIPTIVE  MINERALOGY 


213 


is  an  Important  source  of  silver.  Galena  with  curved  surfaces  is  apt  to 
carry  higher  silver  values  than  that  with  a  good  cubical  cleavage.  Anti- 
mony, iron,  zinc,  gold,  or  bismuth  may  also  be  present.  Alters  to  cerus- 
site,  anglesite,  and  pyromorphite. 

Found  in  veins  in  crystalline  rocks  associated  with  sphalerite,  chal- 
cocite,  bournonite,  quartz,  various  silver  ores,  calcite,  and  barite;  often 
silver  bearing.  Thus,  at  Wallace,  Idaho;  Leadville,  Colorado;  Tintic 
and  Park  City  Districts,  Utah;  Freiberg,  Saxony;  Pribram,  Bohemia, 
Cumberland,  England;  Mexico;  Chile.  Also  in  large  quantities  in 


FIG.  452. — Galena  showing  cubical 
cleavage. 


FIG.  453. — Galena  (light). 
Flat  River,   Missouri. 


Missouri,  Illinois,  Kansas,  Wisconsin,  and  Iowa,  in  non-argentiferous 
veins,  irregular  deposits,  or  replacement  deposits  in  limestones,  with 
calcite,  sphalerite,  chalcopyrite,  smithsonite,  and  marcasite.  Excellent 
crystals  occur  at  Joplin,  Missouri,  and  Mineral  Point,  Wisconsin. 

Galena  is  the  chief  source  of  metallic  lead.     It  is  also  a  valuable  silver 
ore.     Metallic  lead -is  used  extensively  in  the  manufacture  of  paint,  pipes 
and  sheets,  shot,  solder,  type  metal,  easily  fusible  alloys,  and  the  various 
compounds  of  lead. 
Argentite  (Silver  Glance},  Ag2S. 

Cubic,  hexoctahedral  class.  Crystals  are  cubic,  octahedral,  or 
rhombic  dodecahedral  in  habit,  often  distorted  and  in  parallel  groups 
(Fig.  454).  Crystals  are,  however,  not  common.  Generally  dis- 
seminated, coatings,  or  arborescent. 

Hardness  2  to  2.5.  Specific  gravity  7.2  to  7.4.  Malleable,  sectile; 
takes  an  impression.  On  fresh  surface  high  metallic  luster,  but  on  ex- 
posure soon  becomes  dull  and  black.  Dark  lead  gray  color.  Shiny 
lead  gray  streak. 

Commonly  in  veins  associated  with  silver,  cobalt,  and  nickel  minerals; 
proustite,  pyrargyrite,  smaltite,  niccolite,  native  silver.  Occurs  at  Com- 


214 


MINERALOGY 


stock  Lode  and  Tonopah,  Nevada;  Aspen,  Colorado;  Cobalt  district, 
Ontario;  Guanajuata  and  Batopilas,  Mexico;  Freiberg,  Saxony;  Joach- 
imsthal,  Bohemia;  Peru;  and  Chile. 
An  important  ore  of  silver. 

.  Clausthalite,    PbSc;    Altaite,    PbTe;   Hessite,  Ag2Te, 
also  belong  to  the  galena  group. 

CHALCOCITE  (Copper  Glance},  Cu2S. 

Orthorhombic,  bipyramidal  class.  Crystals 
are  tabular  or  thick  prismatic  and  pseudohexa- 
gonal,  the  prism  angle  being  119°  35'  (Figs.  455 
and  456).  Striated  parallel  to  the  a  axis.  Fre- 
quently twinned.  Crystals  not  common.  Usu- 
ally massive, — compact,  granular,  or  disseminated. 
Hardness  2.5  to  3.  Specific  gravity  5.5  to 
5.8.  High  metallic  luster  on  fresh  surface,  which 
soon  becomes  dull  and  black.  Conchoidal  frac- 
ture. Color  dark  lead  gray,  often  tarnished  blue  or  greenish.  Shiny  lead 
gray  streak. 

Cu2S,  usually  with  varying  amounts  of  iron;  also  gold   and  silver. 
Alters  to  covellite,  malachite,  and  azurite. 

Commonly  found  in  veins  with  bornite,  chalcopyrite,    tetrahedrite, 
galena,  enargite,  pyrite,  and  covellite.     Found  in  large  quantities  in  the 


FIG.    454. — Argentite. 
Batopilas,   Mexico. 


FIG.  455. 


FIG.  456. — Chalcocite. 
Cornwall,  England. 


Butte  district,  Montana;  Kennecott,  Copper  River  district,  Alaska; 
Nevada;  Arizona;  Sonora,  Mexico;  excellent  crystals  at  Cornwall, 
England,  and  Bristol,  Connecticut;  as  an  impregnation  at  Mansfield, 
Germany. 

Chalcocite  is  an  important  ore  of  copper. 

Other  members  of  the  chalcocite  group  ore:  Stromeyerite  (Cu,  Ag)2S,  and  Petzite 
(Ag,  Au)2Te. 

CINNABAR  (Natural  Vermilion),  HgS. 

Hexagonal,  trigonal    trapezohedral  class.     Extremely   small,  highly 
modified  crystals;  rhombohedral  or  thick  tabular  in  habit.     Trigonal 


DESCRIPTIVE  MINERALOGY  215 

trapezohedral  faces  are  rarely  observed.  Usually  in  fine  grained  masses, 
crystalline  crusts,  or  powdery  coatings. 

Hardness  2  to  2.5.  Specific  gravity  8  to  8.2.  Adamantine  to  dull 
luster.  In  thin  plates  transparent,  otherwise  opaque.  Color  varies 
with  impurities  and  structure  and  may  be  scarlet,  brownish  red,  brown, 
black,  or  lead  gray.  Scarlet  to  reddish  brown  streak.  If  moistened 
with  HC1  and  rubbed  on  clean  copper,  silver  white  streaks  are  produced. 

HgS,  may  contain  bitumen,  clay,  ferric,  oxide,  etc. 

Cinnabar  is  found  in  veins,  disseminated,  or  in  irregular  masses  in 
sedimentary  rocks,  quartzites,  trachytes,  porphyries,  and  serpentine. 
Usual  associates  are  native  mercury,  pyrite,  marcasite,  realgar,  calcite, 
stibnite,  quartz,  and  opal.  In  sandstones  at  Almaden,  Spain;  in  shales 
and  dolomites  at  Idria,  Austria;  Moschellandsberg,  Bavaria;  excellent 
crystals  in  Kweichow,  China;  Chile;  Peru;  in  serpentine  at  New  Almaden, 
Altoona,  and  New  Idria,  California;  also  Terlinqua,  Texas. 

Cinnabar  is  the  chief  source  of  metallic  mercury  which  is  used  ex- 
tensively in  commerce  and  industry. 

Covellite,  CuS,  an  indigo  blue  copper  mineral,  is  closely  related  to  cinnabar  in 
composition  and  crystallization.  Found  with  other  copper  minerals. 

(6)  Sulpho-minerals 

Most  of  the  important  sulpho-minerals  can  be  referred  to  two  general 
formulas  : 

(a)  M'Jf'tS,  (b) 


2+3  2+5 

In  these  formulas  M'  is  principally  Cu,  Ag,  and  Pb,  while  R'"  may 
be  ferric  iron,  arsenic,  and  antimony.  In  the  second  formula,  R*  is 
pentavalent  arsenic. 

(a)  General  formula  M  'XR"  '2SX 

2  +  3 

Six  minerals  with  these  general  compositions  will  be  described. 


FIG.  457.  FIG.  458. 

CHALCOPYRITE   (Copper  Pyrites,    Yellow  Copper  Ore),  Cu2Fe«S4. 

Tetragonal,  bisphenoidal  class.  Bisphenoidal  crystals  resembling 
octahedrons,  often  distorted  and  difficult  to  interpret  (Figs.  457,  458 
and  459),  Commonly  in  compact  or  disseminated  masses  (Fig.  460). 


216 


MINERALOGY 


Uneven  fracture.  Hardness  3.5  to  4.  Specific  gravity  4.1  to  4.3. 
Brass  to  golden  yellow  in  color.  Tarnishes  to  various  blue,  purple,  and 
blackish  tints;  often  iridescent.  Greenish  black  streak. 

Cu2Fe2S4,  contains  at  times  small  but  valuable  amounts  of  gold  and 
silver;  also  selenium,  thallium,  and  arsenic. 


FIG.  459. — Chalcopyrite  crystals. 
French  Creek,  Pennsylvania. 


FIG.  460. — Chalcopyrite  (dark)  with 
quartz.     Bruce  Mine,  Canada. 


Most  common  copper  mineral.  Usually  with  pyrite,  sphalerite, 
bornite,  galena,  tetrahedrite,  chalcocite,  malachite,  azurite,  quartz, 
and  calcite.  Occurs  at  Falun,  Sweden;  Rio  Tinto,  Spain;  Cornwall, 
England;  Sudbury  district,  Canada;  Chile;  Butte  district,  Montana; 
Bingham,  Utah;  Bisbee,  Arizona;  Ducktown,  Tennessee;  California; 
French  Creek,  Pennsylvania. 

An  important  ore  of  copper. 

BORNITE  (Purple  Copper  Ore,  Horse  Flesh  Ore),  CuxFe2Sa:      . 

2+S 

Cubic,  hexoctahedral  class.  Cubic  and  rhombic  dodecahedral 
crystals;  very  rare.  Commonly  in  compact  and  granular  masses. 

Uneven  fracture.  Hardness  3.  Specific  gravity  4.9  to  5.2.  Metallic 
luster.  Color  on  fresh  fracture  surface  is  between  bronze  and  copper 
red,  tarnishing  readily  and  showing  brilliant  peacock  colors.  Streak  gray 
black. 

Cua.Fe2Sx      ,  where  x  is  commonly  6,  10,  or  12. 

2  +  3 

Frequently  contains  small  amounts  of  gold  and  silver. 

Occurs  with  chalcopyrite,  chalcocite,  enargite,  and  other  copper 
minerals;  also  with  cassiterite,  pyrite,  and  siderite.  Not  very  common 
in  Europe.  Good  crystals  at  Cornwall,  England,  and  Bristol,  Con- 
necticut. In  large  quantities  in  the  Butte  district,  Montana;  Virginia; 
North  Carolina;  Acton,  Canada;  Chile;  Peru;  Bolivia. 

An  important  copper  ore. 


DESCRIPTIVE  MINERALOGY 


217 


PROUSTITE  (Light  Ruby  Silver  Ore,  Light  Red  Silver  Ore],  Ag6As2S6. 
Hexagonal,   ditrigonal   pyramidal   class.     Crystals   often  small,   highly 
modified,  and  difficult  to  interpret.     Hemimorphic  development  some- 
times distinct.     Generally  massive, — disseminated,  in  crusts,  or  bands. 

Conchoidal  fracture.  Hardness  2.5.  Specific  gravity  5.5  Brilliant 
adamantine  to  dull  luster.  Translucent  to  transparent.  Color  and 
streak  scarlet  to  vermilion. 

Ag6As2S6,  at  times  contains  some  antimony. 

Occurs  with  pyrargyrite  in  veins  with  other  silver  minerals,  galena, 
and  calcite.  Occurs  at  Freiberg,  Saxony;  Joachimsthal,  Bohemia; 
Chanarcillo,  Chile;  Guanajuato,  Mexico;  Peru;  Cobalt,  Canada; 
various  places  in  Colorado;  Nevada;  Idaho;  Arizona. 

An  ore  of  silver. 

PYRARGYRITE  (Dark  Ruby  Silver  Ore,  Dark  Red  Silver  Ore),  Ag6-Sb2S6. 

Hexagonal,  ditrigonal  pyramidal  class.  Crystals  resemble  those 
of  proustite;  rare.  Usually  massive, — compact,  disseminated,  crusts,  or 
bands. 

Conchoidal    fracture.     Hardness    2.5    to    3.     Specific    gravity    5.8. 
Metallic  adamantine  luster.     Dark  red  to  lead  gray  in  color;  thin  splin- 
ters in  transmitted  light  are  deep  red.     Cherry  to  purple  red  streak. 
Ag6Sb2S6,  usually  contains  a  little  arsenic. 
Occurrence  similar  to  that  of  proustite  but 
more  abundant.      Found  in  veins  with  other 
silver  ores,  calcite,  and  galena.     Thus,  in  the 
Freiberg  district,  Saxony;  Pribram,  Bohemia ; 
Guanajuato    and    Sonora,    Mexico;    Chile; 
Colorado;     Nevada;     Ari- 
zona; Cobalt,  Ontario. 

An    important    ore    of 
silver. 


FIG.  462. — Bournonite  (cog- 
wheel ore)  and  sphalerite. 
Kapnik,  Hungary. 


FIG.  461. — Bour- 
nonite. Pribram, 
Bohemia. 


BOURNONITE  (Cog-wheel 
Ore),  Pb2Cu2Sb2S6. 

Orthorhombic,   bipyra- 
midal  class.    Thick  tabular 
and  prismatic  crystals  (Fig. 
461).      Frequently   twinned,   forming  cross  or  cog-wheel  crystals  (Fig. 
462).     Also  in  compact  and  granular  masses. 

Hardness  2.5  to  3.     Specific  gravity  5.7  to  5.9.     On  fresh  fracture 
surface  greasy.     Metallic  luster;  crystals  are  sometimes  dull.     Steel-gray 
to  iron  black  in  color.     Dark  gray  to  black  streak. 
Pb2Cu2Sb2S6,  usually  contains  -some  arsenic. 

Occurs  in  veins  with  galena,  sphalerite,  stibnite,  chalcopyrite,  tetra- 
hedrite,  siderite,  and  chalcocite  at  Freiberg,  Saxony;  Pribram,  Bohemia; 


218  MINERALOGY 

Kapnik,  Hungary;  Mexico;  Chile;  Bolivia;  excellent  large  crystals  at 
Park  City,  Utah;  Yavapai  County,  Arizona;  Montgomery  County, 
Arkansas. 

An  ore  of  lead  and  copper. 

The  following  minerals  also  belong  to  this  group;  Miargyrite,  Ag2Sb2S4;  Jame- 
sonite,  Pb2Sb2S5;  Stephanite,  AgioSb2S8;  Pearceite  (Ag,Cu)i6As2Sii;  Polybasite 
(Ag,Cu)i8Sb2Si2. 

TETRAHEDRITE  (Gray  Copper  Ore),  M'8  R'"2S7. 

Cubic,  hetetrahedral  class.  Excellent  crystals  showing  tetrahedral 
development  (Figs.  463,  464,  and  465),  often  highly  modified.  Com- 
monly massive, — compact,  granular,  disseminated. 


FIG.  463.  FIG.  464.  FIG.  465. — Tetrahedrite  with 

quartz.     Kapnik,  Hungary. 

Uneven  fracture.  Hardness  3  to  4.  Specific  gravity  4.3  to  5.4. 
Metallic  luster,  sometimes  dull.  Opaque.  Steel  gray  to  iron  black 
color,  often  with  tarnish  colors.  At  times  coated  with  chalcopyrite  or 
sphalerite.  Streak  black,  or  reddish  brown. 

Composition  varies  greatly,  M '  being  usually  replaced  to  large  extent 
by  lead,  copper,  mercury,  silver,  iron,  or  zinc;  R'"  indicates  antimony  and 
arsenic,  depending  upon  composition.  The  following  varieties  are  often 
differentiated, — cupriferous  and  arsenical,  tennantite;  argentiferous, 
freibergite;  mercurial,  schwatzite. 

Occurs  commonly  in  veins  with  chalcopyrite,  sphalerite,  galena, 
bournonite,  pyrite,  quartz,  siderite,  and  barite.  Found  at  Freiberg, 
Saxony;  Clausthal,  Hartz  Mountains;  Pribram,  Bohemia;  Kapnik, 
Hungary;  Mexico;  Chile;  Peru;  Bolivia;  excellent  crystals  at  Birigham, 
Utah;  many  places  in  Colorado;  Montana;  Nevada;  and  Arizona. 

An  important  ore  of  copper  and  silver. 

(b)  General  Formula,  M^R^'aS 

!+« 

Only  one  mineral  with  a  composition  conforming  to  the  above  formula 
is  sufficiently  common  to  warrant  a  description. 

ENARGITE,    Cu6As2S8. 

Orthorhombic,  bipyramidal  class.  Small  prismatic,  crystals,  vertic- 
ally striated;  rare.  Usually  in  compact,  granular,  or  columnar  masses. 


DESCRIPTIVE  MINERALOGY 


219 


Perfect  prismatic  cleavage.  Uneven  fracture.  Hardness  3.  Specific 
gravity  4.4.  Submetallic  luster.  Grayish  black  to  iron  black  in  color. 
In  artificial  light  resembles  sphalerite.  Streak  black.  Opaque. 

Cu6As2S8,  may  contain  some  iron,  zinc,  and  antimony. 

In  veins  with  other  copper  minerals,  such  as  chalcopyrite,  bornite, 
chalcocite,  tetrahedrite,  also  pyrite.  Not  common  in  Europe.  More 
extensive  in  Peru;  Argentina;  Chile;  Bolivia;  Mexico;  Island  of  Luzon, 
Philippines;  in  large  quantities  in  the  copper  mines  at  Butte,  Montana; 
also  in  San  Juan  Mountains,  Colorado;  Tintic  district,  Utah. 

A  very  important  ore  of  copper.     Also  a  source  of  arsenious  oxide. 


3.   OXIDES  AND  HYDROXIDES       . 

Aside  from  water,  thirteen  minerals  of  this  group  will  be  described. 

1.  OXIDES 


WATER 
QUARTZ 


RUTILE 
ZIRCON 
CASSITERITE 


H20 
Si02 

RUTILE  GROUP 

TiTi04 
ZrSi04 
TiTiO4 


Hexagonal 
Hexagonal 


Tetragonal 
Tetragonal 
Tetragonal 


Pyrolusite 
Zincite 


CORUNDUM 
HEMATITE 


MnO2 
ZnO 

HEMATITE  GROUP 

A1203 
Fe2O3 


Hexagonal 


Hexagonal 
Hexagonal 


CUPRITE 


OPAL 

MANGANITE 
BAUXITE 
LIMONITE 


Cu2O 

2.  HYDROXIDES 

SiO2xH2O 
MnO   OH 
A120.(OH)4 
Fe2O3.H2O 


Cubic 


Amorphous 
Orthorhombic 

Amorphous 


(a)  Oxides 

Many  of  these  minerals  are  very  common  and  of  great  economic 
importance. 

WATER,    Snow,  Ice,   H2O. 

Above  0°C.  water  is  a  liquid,  hence,  amorphous.     It  is  almost  color- 
less, but  in  large  quantities  and  when  pure,  it  has  a  bluish  tinge.     Specific 


220 


MINERALOGY 


gravity,  when  pure,  at  4°C.  and  760  mm.  barometric  pressure  is  1; 
that  of  ocean  water  may  be  as  high  as  1.028.  When  pure  it  is  without 
taste  or  odor. 

Water  occurs  very  widely  distributed  in  nature  and  is  an  important 
agency  in  the  disintegration,  decomposition,  transportation,  and  forma- 
tion of  minerals.  Nearly  all  minerals  are  more  or  less  soluble  in  water, 
especially  if  it  contains  carbon  dioxide,  humus  acid,  hydrochloric  acid, 
or  oxygen  in  solution.  The  ocean  water  contains  about  3.4  per  cent,  of 
solid  matter  in  solution.  Over  thirty  elements 
are  found  in  ocean  water  and,  hence,  water  is  fre- 
quently  called  the  universal  solvent.  When 
water  freezes  it  expands,  the  increase  in  volume 
{  ^_  ~%'j  being  about  9  to  10%  and  the  pressure  exerted 

IBIr  JL  ^Bpr  about  138  tons  per  square  foot.  Due  to  this 
enormous  pressure,  freezing  water  is  a  most  im- 
portant geological  agency,  causing  the  widening 
of  cracks  and  crevices  thereby  extending  the 
zone  of  activity  of  water  and  oxygen  and  hasten- 
ing weathering  and  decomposition. 

On  freezing,  water  forms  snow  or  ice.  Snow  crystals  are  often  very 
beautiful.  They  are  tabular  and  hexagonal  in  outline  (Fig.  466),  and 
show  great  diversity  in  development.  Lake  or  stream  ice  consists  of 
crystals  arranged  in  a  definite  manner,  the  c  axes  being  perpendicular 
to  the  extent  of  the  sheet  of  ice.  In  glacier  ice,  however,  the  ice  particles 
do  not  possess  a  definite  orientation. 

QUARTZ,  SiO2. 

Hexagonal,  trigonal  trapezohedral  class  (below  575°C.).  Crystals 
are  very  common.  They  usually  consist  of  an  hexagonal  prism,  which 


FIG.  466. — Snow  crystal. 
(After  Bentley}. 


FIG.  467. — Quartz  crystals — pyramidal,  prismatic,  long  prismatic,  tabular,  skeletal. 

predominates,  terminated  by  faces  of  a  positive  and  negative  rhombo- 
hedron  so  developed  as  to  simulate  the  hexagonal  bipyramid  of  the  first 
order.  The  pyramidal  habit  is  less  frequent.  The  prism  faces  are  gener- 
ally horizontally  striated  (Fig.  467).  Crystals  are  sometimes  bent, 
twisted,  or  greatly  distorted.  Quartz  forms  right-  and  left-handed 
crystals,  which  are  easily  recognized  when  faces  of  the  trigonal  trapezo- 


DESCRIPTIVE  MINERALOGY 


221 


hedron  are  present  (Fig.  468  left,  Fig.  469  right).  Twins  are  common. 
Figure  470  illustrates  the  common  or  Dauphine  law,  the  vertical  axis 
being  the  twinning  axis.  Here  two  right-  or  left-hand  crystals  inter- 
penetrate so  that  the  positive  rhombohedron  of  the  one  individual 
coincides  with  the  negative  of  the  other,  the  c  axis  being  the  twinning  axis. 
Crystals  twinned  according  to  the  Brazilian  law  (Fig.  471)  consist  of 
a  right-  and  a  left-hand  individual  of  the  same  sign  so  interpenetrated 


FIG.  468. 


FIG.  469. 


FIG.  470. 


FIG.  471. 


that  the  twinned  crystals  are  symmetrical  to  planes  parallel  to  faces  of 
the  prism  of  the  second  order.  Twins  according  to  several  other  laws  are 
not  uncommon.  Crystals  sometimes  show  a  skeletal  development 
(Fig.  472). 

At  times  crystals  contain  scales  of  mica  or  hematite  distributed  in  a 
regular  manner,  so  that  they  may  be  separated  into  sections  or  layers. 


FIG.  472. — Skeletal  quartz. 
Paris,  Maine. 


FIG.  473. — Scepter  quartz  with  phan- 
tom.    Mursink,  Ural  Mountains. 


Such  crystals  are  called  cap  quartz.  Parallel  growths  called  scepter 
quartz  (Fig.  473)  are  also  observed.  Although  quartz  is  commonly 
found  in  distinct  crystals,  it  also  occurs  in  a  great  variety  of  massive  forms. 
Conchoidal  fracture.  Hardness  7.  Specific  gravity  2.65.  Vitreous 
luster.  Transparent  to  opaque.  Commonly  colorless  or  white,  also 
yellow,  red,  pink,  amethystine,  green,  blue,  brown,  and  black.  Many 
colors  disappear  on  heating.  Streak  white. 


222 


MINERALOGY 


SiO2.  Often  contains  inclusions  of  rutile,  hematite,  chlorite,  mica, 
and  liquid  and  gaseous  carbon  dioxide.  Not  attacked  by  the  common 
acids,  and  infusible  before  the  blowpipe.  Common  as  a  pseudomorph 
after  fluorite,  calcite,  siderite,  and  wood. 

The  many  varieties  of  quartz  are  most  conveniently  classified  as, 
(a)  crystalline,  (6)  cryptocrystalline,  and  (c)  clastic. 


FIG.  474. — Quartz,     Dauphine,   France. 


FIG.  475. — Smoky  quartz  with 
muscovite.     Paris,  Maine. 


(a)  Crystalline  varieties  are  vitreous,  either  crystals  or  crystalline 
masses,  and  but  slightly  acted  upon  by  potassium  hydroxide. 

1.  Rock  Crystal. — Colorless  quartz.     Excellent  crystals  are  common 
(Fig.  474). 

2.  Amethyst. — Various  shades  of  purple  or  violet. 

3.  Rose  Quartz. — Pink  to  rose  red  in  color,  becoming  paler  on  exposure 
to  light.     Usually  massive. 

4.  Smoky  Quartz. — Smoky  yellow  to  dark 
brown.     Often  called  cairngorm  stone  (Fig. 
475). 

5.  Milky  Quartz. — Milk-white   in   color. 
Translucent  or  nearly  opaque.     Often  with 
a  greasy  luster. 

6.  Yellow  Quartz. — Light  yellow  in  color, 
often   called  false   topaz,  Spanish  topaz,   or 
citrine. 

7.  Aventurine.  —  Contains    glistening 
scales  of  mica  or  hematite. 

8.  Ferruginous  Quartz. — Brown  or  red  in  color,  due  to  the  presence 
of  either  limonite  or  hematite. 

9.  Rutilated  Quartz. — Contains  fine  interlacing  needles  of  rutile. 

10.  Cat' s  Eye. — Grayish  or  brownish,   with  an  opalescence  due  to 
inclusions  of  fibers  or  to  a  fibrous  structure. 


FIG.  476. — Chalcedony  (stalac- 
titic).     Havana,  Cuba. 


DESCRIPTIVE  MINERALOGY 


223 


11.  Tiger's  Eye. — Yellow  brownish  in  color.  Pseudomorphous  after 
crocidolite.  Pronounced  chatoyant  luster. 

(b)  Cryptocrystalline  varieties  are  compact  and  under  the  microscope 
show  a  crystalline  structure.  More  readily  acted  upon  by  potassium 
hydroxide  than  the  crystalline  varieties. 

1.  Chalcedony. — A  transparent  to  translucent  variety  having  a  waxy 
luster.  Commonly  stalactitic  (Fig.  476),  botryoidal,  concentionary, 
and  lining  cavities.  White,  grayish,  brown,  blue,  and  black  in  color. 


FIG.  477. — Agate.     South  America. 


FIG.  478. — Agate.     Brazil 


2.  Carnelian  or  Sard. — Commonly  reddish  chalcedony. 

3.  Chrysoprase. — Apple-green  chalcedony. 

4.  Heliotrope. — Bright  or  dark  green  chalcedony  with  small  spots  of 
red  jasper  resembling  drops  of  blood.     It  is  often  called  bloodstone. 

5.  Agate. — This  is  chalcedony  made  up  of  strata  or  bands  indicating 
various  stages  of  deposition.     The  layers  may  be  differently  colored  or 


FIG.  479. — Agates — moss,  banded,  cameo.          FIG.  480. — Agate  with  onyx  in  center. 

clouded,  giving  rise  to  several  varieties,  such  as  banded,  moss,  and  clouded 
agates. 

The  banding  is  usually  in  parallel,  but  more  or  less  wavy  or  irregular 
lines  (Figs.  477,  478,  and  479).  Agates  may  be  white,  pale  to  dark 
brown,  or  bluish  in  color.  They  are  frequently  colored  artificially. 

6.  Onyx. — Banded  agate  with  the  bands  or  layers  in  parallel  straight 
lines,  corresponding  to  layers  in  even  planes  (Fig.  480). 

7.  Jasper. — Opaque,  and  red,  yellow,  and  grayish  in  color. 


224  MINERALOGY 

8.  Flint. — Gray,  smoky  brown,  or  brownish   black  in  color.     Com- 
monly in  nodules  with  a  white  coating  (Fig.  481).     Translucent.     Prom- 
inent conchoidal  fracture. 

9.  Chert. — Includes  varieties  with  a  horn-like  appearance,  also  im- 
pure flints  and  jaspers. 

(c)  Clastic  varieties  of  quartz  include  many  of  the  silicious  fragmental 
rocks.     In  some  cases  the  individual  particles  are  no  longer  distinct. 

1.  Sand. — Loose,    unconsolidated    grains    or    fragments    of    quartz. 

2.  Sandstone. — Consolidated  sand.     The  cementing  material  may  be 
silica,  iron  oxide,  calcium  carbonate,  or  clay.     Occurs  in  a  great  variety 
of  colors. 

3.  Itacolumite. — A  flexible  sandstone.     Contains  some  mica. 

4.  Quartzite  or  Granular  Quartz. — Metamorphosed  sandstone  in  which 

the  cement  is  silica.  The  individual  quartz  parti- 
cles are  generally  not  easily  recognized  by  the  naked 
eye. 

Next  to  water,  quartz  is  the  most  common  of  all 
oxides.  It  is  a  very  important  rock-forming 
mineral,  being  a  primary  constituent  of  many 
igneous  and  sedimentary  rocks,  and  occurs  in  rocks 
of  all  ages  and  in  many  ore  deposits.  It  is  also 
found  very  abundantly  as  sand  and  gravel. 

Rock  crystal,  amethyst,  smoky  and  rose  quartz, 


FIG    481 —Flint     aventurine,  cat's  eye,  tiger's  eye,  chalcedony,  agate, 
Dover  cliffs,  England,    and  jasper  are  used  rather  extensively  in  jewelery 
and  for  ornamental  purposes;  agate  and  chalcedony 
for  mortars  and  pestles;  rock  crystal  for  dishes,  vases,  optical  instru- 
ments,  spectacles,   and  chemical  apparatus;  sand  for  mortar,  plaster, 
glass,  and  sandpaper;  sandstone  and  quart zite  for  building  and*  paving 
purposes,  and  grindstones;  and  ground  or  crushed  quartz  and  flint  in 
wood  fillers,  pottery,  scouring  and  polishing  soaps,  and  as  an  abrasive. 
Large    quantities    of  quartz  are  also  used  as  a  flux  in  metallurgical 
processes. 

Rutile  Group 

This  group  contains  the  three  common  oxides  of  titanium,  tin,  and 
zirconium  and  silicon,  which  crystallize  in  the  tetragonal  system. 

RUTILE,  TiTiO  4. 

Tetragonal,  ditetragonal  bipyramidal  class.  Crystals  are  common. 
Usually  prismatic  or  thick  columnar,  consisting  of  the  prisms  and  bi- 
pyramids  of  the  first  and  second  orders  (Fig.  482) .  Prism  faces  frequently 
striated  vertically  (Fig.  483a).  Knee-shaped  twins  often  observed, 
the  twinning  plane  being  parallel  to  a  face  of  the  bipyramid  of  the  second 


DESCRIPTIVE  MINERALOGY 


225 


order  (Fig.  4836).  Also  trillings,  sixlings,  and  eightlings  (rosettes)  ac- 
cording to  this  law  (Fig.  483c).  Also  in  compact,  granular  masses. 
Needle-like  crystals  of  rutile  occur  frequently  as  inclusions  in  quartz. 

Distinct  prismatic  and  pyramidal  cleavages.  Hardness  6  to  6.5. 
Specific  gravity  4.2  to  4.3.  Metallic  adamantine  luster.  Opaque  to 
transparent.  Red  brown,  blood  red,  and  black  in  color.  Streak  yellow 
or  pale  brown. 

TiTiO4,  sometimes  written  Ti02.  Usually  contains  considerable  iron. 
Occurs  pseudomorphous  after  hematite,  brookite,  and  anatase. 

Rutile  is  the  most  common  titanium  mineral  and  occurs  in  gneiss, 
mica  schists,  granite,  granular  limestone,  and  dolomite.  Commonly 
associated  with  quartz,  hematite,  and  feldspar.  Found  at  Arendal  and 
Kragero,  Norway;  Ural  Mountains;  Binnenthal  and  St.  Gothard  dis- 


FIG.  482. — Rutile.     Georgia. 


FIG.  483. — Rutile  crystals — (a) 
prismatic  and  striated,  (&)  knee- 
shaped,  (c)  rosette  (Eightling). 


trict,  Switzerland;  Nelson  County,  Virginia;  Graves  Mountain,  Georgia; 
Magnet  Cove,  Arkansas.  Occurs  also  in  secondary  deposits  with  quartz, 
tourmaline,  gold,  and  diamond. 

Used  in  coloring  porcelain  yellow  and  artificial  teeth  bluish  (pinkish) 
white;  also  in  special  grades  of  steel  and  copper-bearing  alloys;  as  a 
mordant  in  dyeing  leather,  and  in  carbons  for  arc  lights. 

ZIRCON,  Hyacinth,  Jargon,  ZrSiO4. 

Tetragonal,  ditetragonal  dipyramidal  class.  Usually  in  simple, 
well-developed  crystals,  consisting  of  the  prism  and  bipyramid  of  the 
first  order  (Fig.  484);  more  complex  crystals  sometimes  observed  (Fig. 
485).  Also  as  rounded  or  angular  lumps  or  grains  in  sands  and  gravels. 

Hardness  7.5.  Specific  gravity  4.4  to  4.8.  Adamantine  luster. 
Transparent  to  opaque.  Commonly  brown  or  grayish,  also  red,  yellow, 
and  colorless.  Transparent.  Reddish  and  brownish  varieties  are  often 
called  hyacinth  or  jacinth;  when  colorless  and  smoky,  jargon.  Cut  stones 
possess  good  brilliancy  and  fire, 

15 


226 


MINERALOGY 


ZrSi04.  Often  interpreted  as  a  silicate.  Usually  contains  a  small 
amount  of  iron. 

Occurs  disseminated  in  the  more  acid  igneous  rocks,  especially  granites 
and  syenites;  also  found  in  gneiss,  schists,  and  crystalline  limestone. 
Occurs  in  nephelite-syenite  in  southeastern  Norway;  Miask,  Ural  Moun- 
tains (Fig.  486);  Wichita  Mountains,  Oklahoma;  Litchfield,  Maine. 


FIG.  484. 


FIG.  486. — Zircon  in  syenite. 
Ilmensk,  Ural  Mountains. 


Common  in  the  sands  and  gravels  of  Ceylon,  also  in  Henderson,  Irdell, 
and  Buncombe  counties  of  North  Carolina. 

Zircon  is  a  source  of  ZrO2,  which  is  used  in  limited  amounts  in  Nernst 
lamp  glowers.  Hyacinth,  jacinth,  and  jargon  are  cut  as  gems.  The  color- 
less zircon  from  Matura,  Ceylon,  is  often  called  matura  diamond. 

CASSITERITE  (Tin  Stone),  SnSnO4. 

Tetragonal,    ditetragonal   bipyramidal  class.     Crystals  are   usually 

short  prismatic,  showing  the  prisms  and  bipyramids  of  the  first  and 

second  orders,  similar  to  those  of  zircon. 
Knee-shaped  twins  are  common,  the  bi- 
pyramid  of  the  second  order  being  the 
twinning  plane.  Frequently  in  dissemi- 
nated, granular,  or  reniform  masses;  also 
in  grains  and  pebbles.  Concentric  and 
fibrous  radial  structure  is  frequently  ob- 
served. 

Hardness    6    to    7.     Specific    gravity 
6.8    to    7.     Adamantine    to    submetallic 

luster.     Reddish    brown,    brown,  black;  also  yellow  or  white.     Streak 

white  to  pale  brown. 

Three  varieties  may  be  distinguished  : 

1.  Ordinary  Cassiterite  or  Tin  Stone. — Crystals  and  compact  masses. 

2.  Wood  Tin. — Botryoidal  and  reniform  masses  of  varying  colors, 
with  concentric  structure  and  commonly  with  a  radial  fibrous  structure. 

3.  Stream  Tin. — Angular  and  rounded  grains  or  pebbles  in  sands  and 
gravels  of  streams. 


FIG.  487. — Cassiterite  with  fluorite. 
Saxony. 


DESCRIPTIVE  MINERALOGY  227 

SnSnO4,  sometimes  written  SnO2.  Generally  contains  some  iron. 
Infusible  and  insoluble  in  acids. 

Cassiterite  is  commonly  associated  with  quartz,  topaz,  fluorite  (Fig. 
487) ,  apatite,  and  tourmaline.  It  occurs  generally  in  veins  cutting  gran- 
ites and  rhyolites,  which  have  generally  been  greatly  altered  as  the  result 
of  pneumatolytic  action.  Granitic  rocks  altered  in  this  way  are  called 
greisen,  while  non-granitic  rocks  are  termed  zwitter.  On  account  of  its 
great  resistance  to  weathering,  cassiterite  is  also  found  extensively  ill 
secondary  deposits.  The  Malay  Peninsula  of  Malacca,  (the  Straits 
Settlements),  the  islands  of  Banca  and  Billiton  near  Borneo,  and  Bolivia 
are  the  chief  producers  of  cassiterite.  Other  localites  are:  Cornwall, 
England;  Altenberg,  Saxony;  Buck  Creek,  Alaska;  Black  Hills,  South 
Dakota;  Gaffney,  South  Carolina;  Kings  Mountain,  North  Carolina; 
El  Paso,  Texas. 

Cassiterite  is  the  only  source  of  tin  of  commerce  and  industry,  which 
is  used  extensively  in  the  manufacture  of  tin  plate  or  sheet  tin  (sheet 
iron  or  steel  dipped  in  molten  tin),  solder,  bronze,  tin  amalgam,  gun 
metal,  type  metal,  speculum  metal,  Britannia  metals,  and  pewter. 
Sodium  stannate  is  used  in  calico  printing  and  the  artificial  oxide  is  used 
as  a  polishing  powder. 


PYROLUSITE  (Black  Oxide  of  Manganese),  MnO2. 

Prismatic  and  needle-like  crystals  pseudomorphous  after  manganite; 
generally  compact,  fibrous,  columnar,  stala- 
citic,  dendritic,  or  powdery  crusts  (Fig.  488). 

Hardness  1  to  2.5,  soils  the  fingers. 
Specific  gravity  4.8.  Black  or  dark  steel 
gray  in  color.  Black  or  bluish  black  streak. 
Metallic  to  dull  luster.  Opaque. 

Mn02.  Usually  contains  small  amounts 
of  water  and  silica. 

Pyrolusite  is  a  secondary  mineral  result- 
ing from  the  decomposition  of  manganite,  FlG-  488.— Pyrolusite.  lifeid, 

,       .       .          .  .     J          .  Thunngia,  Germany. 

rnodochrosite,     and    various    mangamferous 

iron  ores.     Usually  found  with  manganite,  psilomelane,  hematite,  or 

limonite. 

Occurs  extensively  in  Thuringia  and  in  the  Harz  Mountains,  Ger- 
many; Bohemia;  France;  Brazil;  Russia;  Hungary;  Cuba.  The  principal 
localities  in  the  United  States  are  the  Crimora  district,  Augusta  County, 
Virginia;  Cave  Spring  and  Cartersville,  Georgia;  Batesville,  Arkansas; 
Livermore,  Alameda  County,  California;  Brandon,  Vermont. 

Pyrolusite  is  used  in  the  manufacture  of  chlorine,  bromine,  oxygen, 
f  erromanganese,  manganese  bronze,  and  spiegeleisen ;  as  a  coloring  agent 
in  calico-printing  and  dyeing,  glass,  pottery,  bricks,  and  paints;  also  as  a 


228 


MINERALOGY 


Spiegeleisen  is  of  great 


decolorizer  of  green  glass,  and  in  dry  batteries, 
importance  in  the  metallurgy  of  iron  and  steel. 

ZINCITE  (Red  Zinc  Ore),  ZnO. 

Hexagonal,    dihexagonal   pyramidal   class.     Crystals   are   hemimorphic 

and  consist  of  prisms,  upper  pyramid,  and  lower  basal  pinacoid.     Natural 

crystals  are  very  rare.     Usually  as  compact, 
granular,  or  foliated  masses  (Fig.  489). 

Perfect  basal  cleavage.  Hardness  4  to 
4.5.  Specific  gravity  5. 4  to  5. 7  Subadaman- 
tine  to  vitreous  luster.  Dark  red  to  orange 
or  yellow  in  color.  Reddish  to  orange 
yellow  streak.  Translucent  to  opaque. 

ZnO.  Usually  contains  some  manganese 
and  iron. 

Occurs  extensively  at  Franklin  Furnace, 
Sussex  County,  New  Jersey,  in  metamorphic 

limestones  associated  with  franklinite,  rhodonite,  willemite,   sphalerite, 

rhodochrosite,    and    calcite.     Also   in    Schneeberg,    Saxony;   Tuscany; 

Poland. 

An  important  ore  of  zinc.     It  has  been  used  for  detectors  in  wireless 

apparatus. 

Hematite  Group 

This   group   includes   the   two   very   important   economic   minerals 
corundum  and  hematite.     These  are  the  sesquioxides  of  aluminum  and 
iron,    respectively.      They    crystallize    in 
the  hexagonal  system. 


FIG.  489.  —  Zincite  (dark) 
with  calcite.  Franklin  Furnace, 
New  Jersey. 


CORUNDUM,    Sapphire,    Ruby,    Emery, 
A1203. 

Hexagonal,  ditrigonal  scalenohedral 
class.  Well  developed  crystals  are  com- 
mon, and  often  rather  large.  The  habit 
may  be  pyramidal,  rhombohedral,  pris- 
matic, or  tabular  (Fig.  490).  The  most 
common  forms  are  the  prism  of  the  second 
order,  unit  rhombohedron,  bipyramid  of 
the  second  order,  and  the  basal  pinacoid. 
Large  crystals  are  sometimes  rough  or  •  FlG-  490.— Corundum  crystals 

i     T     ,  ,     ,  ,         .       .  — tabular,     prismatic,      pyramidal, 

rounded,   barrel-shaped,  and  deeply  fur-    iong  prismatic. 

rowed    or    striated.       Penetration    and 

polysynthetic  twins  are  common,  the  twinning  being  parallel  to  the  unit 

rhombohedron.     The  basal  pinacoid  often  shows  triangular  striations. 

Occurs  also  in  compact,  granular,  and  lamellar  masses,  showing  frequently 

a  nearly  rectangular  parting  or  pseudo-cleavage. 


DESCRIPTIVE  MINERALOGY  229 

Basal,  and  nearly  rectangular  rhombohedral  partings.  Conchoidal 
fracture.  Hardness  9.  Specific  gravity  3.9  to  4.1.  Commonly  gray, 
brown,  and  bluish;  also  red,  blue,  yellow,  and  colorless.  Sometimes 
multicolored.  Transparent  to  translucent.  Vitreous  luster. 

A12O3.  Crystals  are  usually  quite  pure.  Small  amounts  of  ferric 
oxide  may  be  present  as  a  pigment.  Emery  is  generally  quite  impure. 

Several  varieties  of  corundum  may  be  distinguished. 

(1)  Ruby. — This  is  the  transparent  deep  red  variety.     It  is  highly 
prized  as  a  gem. 

(2)  Sapphire. — The  sapphire  proper  is  a  transparent  blue  corundum. 
Transparent  stones  of  other  colors  are  called  yellow,  golden,  or  white 
sapphires,   etc.     Sometimes   the  following  terms   are   also   used,   when 
green,    oriental    emerald;    yellow,    oriental    topaz; 

violet,  oriental  amethyst.     Sapphires  are  also  used 
for  gem  purposes. 

(3)  Common  Corundum. — This  includes  crys- 
tals and  compact  masses  with  dull  and  irregularly 
distributed  colors. 

(4)  Emery. — This   is   an  intimate  mixture  of 
corundum,     magnetite,     hematite,     quartz,    and 
spinel.     Dark  gray  to  black  in  color,  and  was  first 
considered  an  iron  ore.     The  admixture  may  be 

as  high  as  40  per  cent.  The  hardness  may  be  considerably  lower  than 
that  of  the  other  varieties,  namely  7  to  9. 

Corundum  occurs  usually  disseminated  in  crystalline  limestone  and 
dolomite  (Fig.  491),  gneiss,  mica  schist,  chlorite  schist,  nepheline  syenite, 
granite,  and  other  crystalline  rocks.  It  is  commonly  associated  with 
magnetite,  mica,  chlorite,  nephelite,  serpentine,  and  spinel. 

The  gem  varieties  are  found  principally  in  placer  deposits  in  Ceylon, 
Burma,  Hindustan,  Siam,  China,  Queensland,  Ural  Mountains,  and  near 
Helena,  Montana.  Rubies  and  sapphires  have  been  highly  prized  as 
gems.  Latterly  they  have  been  produced  synthetically  in  large  quanti- 
ties. Many  of  these  synthetic,  or  reconstructed  sapphires,  as  they  are 
erroneously  called,  possess  superior  colors,  and  when  small  are  often 
extremely  difficult  to  distinguish  from  the  natural  stones. 

Common  corundum  is  found  in  extensive  deposits  associated  with 
peridotite  in  North  and  South  Carolina,  and  Georgia ;  at  Raglan  and  else- 
where in  Renfrew  County,  Ontario,  in  nepheline  syenite;  also  in  West- 
chester  County,  New  York;  Chester  County,  Pennsylvania;  and  Chester 
Massachusetts. 

Most  of  the  world's  supply  of  emery  is  obtained  from  the  islands  of 
Naxos  and  Samos  in  the  Grecian  archipelago,  and  from  Asia  Minor. 
On  Naxos  and  Samos  it  occurs  in  crystalline  limestones  and  schists.  It  is 
also  found  in  the  Ural  Mountains ;  Saxony ;  associated  with  chlorite  and 


230 


MINERALOGY 


margarite  in  amphibolite  schist  at  Chester,  Massachusetts;  in  peridotito 
at  Peekskill,  New  York. 

Ruby  and  sapphire  are  used  extensively  for  gem  purposes  and  as 
jewels  in  watches  and  various  scientific  instruments.  Common  corun- 
dum and  emery  are  important  abrasive  materials. 

HEMATITE,  Specularite,  Specular  Iron  Ore,  Red  Iron  Ore,  Fe2O3. 

Hexagonal,  ditrigonal  scalenohedral  class.  Crystals  are  either  thin  or 
thick  tabular,  pyramidal,  rhombohedral,  or  more  rarely  prismatic  in 


FIG.  492. 


FIG.  493. — Hematite.     Island  of 
Elba. 


FIG.  494. — Specular  hematite. 
Lake  Superior  District.' 


habit  (Figs.  492  and  493) .  Tabular  crystals  are  often  arranged  in  rosettes 
and  are  then  called  iron  roses.  The  basal  pinacoid  is  frequently  striated, 
due  to  polysynthetic  twinning.  Occurs  more  abundantly  in  compact^ 


FIG.  495. — Hematite  (kidney  ore). 
Cumberland,   England. 


FIG.  496. — Micaceous  hematite 
Lake  Superior  District. 


granular  (Fig.  494),  columnar,  fibrous,  botryoidal  (Fig.  495),  reniform, 
stalactitic,  micaceous  (Fig.  496),  oolitic,  and  earthy  masses. 

No  cleavage,  but  a  rhombohedral  parting  which  is  nearly  cubical 


DESCRIPTIVE  MINERALOGY  231 

is  sometimes  observed.  Conchoidal  to  uneven  fracture.  Hardness 
5.5  to  6.5;  earthy  varieties  are  very  soft.  Specific  gravity  4.9  to  5.3. 
Metallic,  splendent,  or  dull  luster.  Opaque,  except  in  very  thin  scales. 
Commonly  steel  gray,  reddish  brown,  or  iron  black  in  color;  sometimes 
with  beautiful  tarnish  colors.  Earthy  varieties  are  red  in  color.  Cherry 
red  or  reddish  brown  streak.  Sometimes  slightly  magnetic,  due  to  the 
presence  of  small  amount  of  magnetite. 

Fe2O3.  May  contain  as  much  as  7  per  cent,  of  titanium  dioxide; 
also  ferrous  oxide,  magnesium  oxide,  phosphoric  acid,  silica,  and  clay. 
Infusible.  Becomes .  magnetic  when  heated  on  charcoal.  When  pow- 
dered it  is  slowly  soluble  in  acids.  Occurs  as  a  pseudomorph  after  cal- 
cite,  siderite,  pyrite,  and  magnetite. 

There  are  several  varieties  of  hematite. 

(1)  Specularite  or  Specular  Iron  Ore. — This  includes  crystals,  micaceous, 
and  granular  masses  with  a  metallic  or  splendent  luster  (Figs.  494  and 
496) .     Usually  steel  gray  or  iron  black  in  color. 

(2)  Compact  or  Red  Hematite. — Compact  masses,  often  with  a  radial 
fibrous  structure.     Submetallic  to  dull  luster.     Iron  black  or  brownish 
red  in  color. 

(3)  Kidney    Ore. — Reniform    masses,    usually    with    smooth    shiny 
surfaces  (Fig.  495). 

(4)  Red  Ocher. — This  includes  earthy  varieties,  which  are  very  soft 
and  have  a  dull  luster.     Often  contains  considerable  clay  or  sand. 

(5)  Argillaceous  Hematite. — Hard  and  compact  varieties,  which  are 
generally  quite  impure  due  to  admixtures  of  much  clay,  sand,  or  jasper. 
Brownish  black,  reddish  brown,  or  red  in  color. 

(6)  Oolitic  or  Fossil  Iron  Ore. — This   variety   possesses   an   oolitic 
structure,  and  frequently  contains  fossil  remains. 

(7)  Martite. — Hematite  occurring  in  octahedrons,  pseudomorphous 
after  magnetite. 

Hematite  is  the  most  important  iron  ore.  It  occurs  (1)  in  independent 
deposits,  sometimes  of  great  thickness  and  extent.  (2)  As  an  accessory 
mineral  in  many  igneous  rocks,  such  as  granite  and  syenite.  (3)  In 
cracks  and  crevices,  usually  with  quartz.  (4)  As  an  inclusion  in  many 
minerals;  thus,  in  feldspar,  quartz,  and  carnallite.  (5)  As  a  sublimation 
product  in  lavas;  thus,  on  Vesuvius  and  Aetna.  (6)  Sometimes  it  is  the 
result  of  contact  metamorphism. 

Excellent  crystals  are  found  on  the  island  of  Elba,  in  the  Mediter- 
ranean Sea;  St.  Gothard  district,  Switzerland  (iron  roses);  Arendal, 
Norway;  Langban  and  Nordmark,  Sweden;  Cumberland,  England. 

Enormous  deposits  of  hematite  occur  in  the  rocks,  chiefly  of  Huronian 
and  Archean  ages,  in  the  Lake  Superior  region  of  Northern  Michigan, 
Minnesota,  Wisconsin,  and  Canada.  There  are  six  well  defined  iron 
ranges  or  districts  in  this  region,  viz;  Marquette  in  Michigan;  Menominee 


232  MINERALOGY 

and  Gogebic  in  Michigan  and  Wisconsin;  Mesabi  and  Vermilion  in  Min- 
nesota; Michipicoten  in  Ontario,  Canada.  In  1919  this  region  produced 
63,735,088  long  tons  of  iron  ore,  of  which  the  greater  part  was  mined  by 
steam  shovels  operating  in  huge  open  pits.  This  ore  includes  both  the 
hard  and  soft  varieties.  Oolitic  or  fossiliferous  hematite  occurs  at 
Clinton,  New  York;  and  in  large  quantities  in  eastern  Tennessee  and 
Northern  Alabama.  Birmingham,  Alabama,  is  the  center  of  this  im- 
portant district.  Important  deposits  of  hematite  also  occur  in  Missouri, 
Wyoming,  and  Pennsylvania. 

Hematite  is  the  chief  source  of  the  iron  of  commerce  and  industry. 
Over  90  per  cent,  of  the  iron  ore  mined  annually  is  hematite. 


CUPRITE   (Ruby    Copper   Ore),  Cu2O. 

Cubic,    pentagonal    icositetrahedral    class.     Crystals    are    common, 
consisting  usually  of  the   cube    (Fig.   497),   octahedron,   and  rhombic 
dodecahedron,    often   in    combination.     Also    compact,    granular,    and 
earthy    massive;    fine    slender    aggregates    are 
called  chalcotrichite  or  plush  copper. 

Hardness  3.5  to  4.  Specific  gravity  5.7  to 
6.1.  Metallic  adamantine  to  dull  luster.  Ruby 
red  to  almost  black  in  color.  Transparent  to 
opaque.  Brownish  red  to  dirty  brown  streak. 

Cu?O.     Usually  quite  pure.     Alters   readily 
to  malachite,  azurite,  tenorite,  and  native  cop- 
per.    Pseudomorphs  of  malachite  after  cuprite 
are  quite  common. 
'IG'  4B^eCUAriztonaUbeS)'  CuPrite  is  a  secondary  mineral,  resulting  from 

the  oxidation  of  various  copper  minerals.  Com- 
monly found  with  malachite,  azurite,  native  copper,  chrysocolla,  limo- 
nite,  and  chalcopyrite. 

At  Chessy,  France,  it  occurs  in  crystals  partially  or  completely  altered 
to  malachite;  also  found  at  Cornwall,  England;  Dobschau,  Hungary; 
Chile;  Peru;  Bolivia;  Ural  Mountains.  Abundant  with  other  copper 
ores  at  Bisbee,  Clifton,  and  Morenci,  Arizona;  with  native  copper  in  the 
Lake  Superior  Copper  district. 
An  important  ore  of  copper. 

(6)  Hydroxides 

Only  the  four  most  important  hydroxides  will  be  described.     These 
minerals  are  generally  of  secondary  origin. 

OPAL,  SiO2.xH2O. 

Amorphous.     Usually  compact,  in  veins  or  irregular  masses  sometimes 
with  botryoidal,  reniform,  stalactitic,  or  earthy  structure. 


DESCRIPTIVE  MINERALOGY 


233 


Conchoidal  fracture.  Hardness  5.5  to  6.5;  in  earthy  varieties  may  be 
as  low  as  1.  Specific  gravity  2.1  to  2.3.  Vitreous,  dull,  or  greasy  luster. 
Transparent  to  opaque.  Streak  white.  Color  varies  greatly;  colorless, 
white,  yellow,  brown,  red,  green,  gray,  blue,  and  so  forth.  Often  beautiful 
play  of  colors  may  be  observed.  This  is  due  to  fine  cracks  filled  with 
material  possessing  a  slightly  different  index  of  refraction  than  the  original 
substance,  and  perhaps  also  to  an  unequal  distribution  of  the  water 
content.  Some  opaque  opals  show  an  opalescence,  especially  after 
immersion  in  H2O. 

SiO2.xH2O.  The  amount  of  water  present  may  vary  from  1  to  21 
per  cent.,  but  is  usually  between  3  and  13  per  cent.  Many  opals  are  to 
be  considered  as  dried  and  hardened  gelatinous  silica.  Yields  water  when 
heated  in  a  closed  tube.  Infusible.  Soluble  in  hot  caustic  potash  or 
soda. 


FIG.  498.— Wood  opal. 
Storlein,  Hungary. 


FIG.  499  . — Opal : 
Variety,  hyalite.  Wal- 
tsch,  Bohemia. 


FIG.  500.— Opal:  Va- 
riety, geyserite.  Yellow- 
stone Park. 


The  principal  varieties  of  opal  include: 

(1)  Precious  Opal. — Yellowish  white,  dark  gray,  or  bluish  in  color 
with  an  excellent  play  of  colors.     Those  with  the  lighter  colors  are  called 
white  opals,  while  the  dark  gray  and  blue  opals  are  designated  as  black 
opals. 

(2)  Fire  Opal. — Orange  yellow  to  red  in  color.     Semi-transparent. 

(3)  Common  Opal. — Translucent  to  opaque  and  shows  many  colors. 
When  milk-white,  yellowish,  bluish,  or  greenish  it  is  called  milk  opal. 
With  a  resinous  luster  and  either  wax,  honey,  or  other  yellow  in  color,  it  is 
resin  opal.     Wood   petrified   by  opaline  material  is   called   wood  opal 
(Fig.  498) .     Opal  jasper  is  red,  reddish  brown,  or  yellow  brown  in  color 
with  a  resinous  luster,  and  resembles  jasper. 

(4)  Hyalite. — Colorless  and  transparent  masses  of  irregular  outline. 
Looks  like  drops  of  melted  glass  (Fig.  499). 


234  MINERALOGY 

(5)  Silicious  Sinter,  Geyserite. — These  are  opaline  deposits  from  hot 
springs  and  geysers.     May  be  porous,  compact,  fibrous,  stalactitic,  or 
botryoidal  (Fig.  500) ;  grayish,  whitish,  or  brownish  in  color,  and  some- 
times possess  a  pearly  luster. 

(6)  Tripolite,    Diatomaceous   or   Infusorial   Earth. — Porous,    earthy, 
and  chalk-like  deposits  of  the  silicious  remains  of  diatoms,  radiolaria, 
and  so  forth.     Light  in  weight. 

Opal  is  commonly  the  result  of  the  decomposition  of  silicate  rocks, 
and  is  hence  frequently  found  in  cracks  and  cavities  in  igneous  and 
sedimentary  rocks.  Common  Opal  occurs  rather  widely  distributed. 
Precious  opal  is  found  at  Czerwenitza, ~ Hungary;  Queretaro,  and  else- 
where in  Mexico;  Humboldt  County,  Nevada;  Latah  County,  Idaho; 
Honduras;  New  South  Wales,  especially  at  White  Cliffs. 

Silicious  sinter  or  geyserite  occurs  abundantly  in  the  Yellowstone 
Park,  Iceland,  and  New  Zealand.  Infusorial  earth  is  found  in  con- 
siderable deposits  at  Richmond,  Virginia;  Drakesville,  New  Jersey; 
Socorro,  New  Mexico. 

Precious  and  fire  opals  are  used  for  gem  purposes;  wood  opal  for 
ornamental  purposes.  Infusorial  earth  and  tripolite  are  used  in  polish- 
ing powders,  scouring  soaps,  artificial  fertilizers,  paint,  wood  fillers,  in 
the  filtering  and  refining  of  sugar,  and  as  non-conductor  of  heat. 

MANGANITE,  MnO(OH). 

Orthorhombic,  bipyramidal  class.  Commonly  in  deeply  striated 
prismatic  crystals,  arranged  in  groups  or  bundles  (Fig.  501).  Also 

in  radial  fibrous  and  columnar  masses,  more 
rarely  granular  and  stalactitic. 

Perfect  brachypinacoidal  cleavage.  Un- 
even fracture.  Hardness  3.5  to  4.  Specific 
gravity  4.3.  When  fresh,  manganite  possesses 
a  submetallic  luster,  an  iron  black  color,  and  a 
reddish  brown  to  brownish  black  streak.  If 
more  or  less  decomposed,  it  is  steel  gray  in 

FIG.  501. — Manganite.    ro]or  wjth    o   hlaplr  <?trp«lr    »r»H  mpfnllip  Incsfpr 
Ilmenau,  Thuringia,  Germany.    C  reaK>  aiK  lUSter. 

MnO.OH.  Soluble  in  concentrated  hydro- 
chloric acid  with  an  evolution  of  chlorine.  Occurs  as  a  pseudomorph 
after  calcite.  Alters  easily  to  pyrolusite. 

Commonly  associated  with  hematite,  barite,  calcite,  siderite,  pyrolu- 
site, and  other  manganese  minerals.  Excellent  crystals  occur  at  Ilfeld, 
Hartz  Mountains;  Ilmenau,  Thuringia;  Langban,  Sweden;  Marquette 
County,  Michigan;  Douglas  County,  Colorado;  Nova  Scotia;  New 
Brunswick;  Cornwall,  England. 

With  pyrolusite  it  is  used  extensively  in  the  preparation  of  oxygen  and 
chlorine. 


DESCRIPTIVE  MINERALOGY 


235 


BAUXITE,  A120(OH)4. 

Crystallization  unknown.  Commonly  shows  a  pisolitic  or  oolitic 
structure  with  rounded,  concretionary  grains  embedded  in  an  amorphous 
or  clay-like  mass  (Fig.  502). 

Hardness  1  to  3.  Specific  gravity  2.55.  May  be  white,  brown, 
yellow,  or  reddish  in  color.  Argillaceous  odor.  Variable  streak.  Dull 
to  earthy  luster. 

Al2O(OH)4.  The  composition  varies  greatly,  aluminum  oxide  being 
as  low  as  40  per  cent,  or  as  high  as  70  per  cent.  Ferric  oxide,  water,  silica, 
and  titanium  oxide  are  usually  present  in  varying  amounts. 

Bauxite  is  a  decomposition  product  of  feldspathic  rocks,  such  as 
granites,  syenites,  gneisses,  etc.,  the  structure  of  the  rocks  being  some- 
times well  preserved.  It  is  one  of  the  principal  constituents  of  laterite, 
which  is  quite  abundant  in  tropical  regions. 
Bauxite  is  also  found  in  nodules,  grains,  and 
pockets  of  irregular  shape  in  limestones  and  dolo- 
mites, probably  the  result  of  deposition  from  hot 
solutions. 

The  most  important  deposits  of  bauxite  in  the 
United  States  are  found  in  Pulaski  and  Saline 
Counties,  Arkansas,  the  town  of  Bauxite  being 
the  chief  center;  also  in  a  belt  extending  from 
Jacksonville,  Alabama,  to  Adamsville,  Georgia, 
Tennessee;  in  the  departments  of  Languedoc  and 
Provence,  southeastern  France;  Nassau,  Germany; 
Ireland. 

Bauxite  is  used  in  the  manufacture  of  aluminum,  alum,  bauxite 
brick,  and  the  artificial  abrasive  called  alundum. 

LIMONITE  (Brown  Hematite),  Fe2O3.H2O. 

Probably  amorphous.  Nearly  always  found  in  compact,  porous,  or 
earthy  masses.  Often  stalactitic  (Fig.  503),  botryoidal,  or  mammillary. 
Radial  fibrous  structure  and  black  varnish-like  surfaces  are  quite  charac- 
teristic (Fig.  504).  Also  concretionary. 

Hardness  1  to  5.5.  Specific  gravity  3.4  to  4.  May  be  yellowish, 
brown,  or  black  in  color.  Streak  always  yellow  brown.  Conchoidal 
to  earthy  fracture. 

Fe2O3.H2O.  Often  impure,  containing  silica,  clay,  manganese 
oxide,  and  organic  matter.  Common  as  a  pseudomorph  after  iron 
minerals,  especially  pyrite,  marcasite,  and  siderite. 

The  important  varieties  are: — 

1.  Com,pact  Limonite. — This  includes  the  compact  massive,  stalactitic, 
botryoidal,  and  other  varieties  which  often  possess  a  radial  fibrous 
structure  and  smooth  varnish-like  surfaces. 


FIG.  502. — Pisolitic 
bauxite.  Linwood,  Geor- 
gia. 


236 


MINERALOGY 


2.  Bog  Iron  Ore. — Found  in  marshy  and  swampy  places.     More  or 
less  loose  and  porous  in  texture  and  may  contain  organic  remains. 

3.  Ochreous  Limonite. — Here  are  placed  the  earthy,  yellow  or  brownish 
varieties,  which  may  be  quite  impure  on  account  of  the  admixture  of 
clay  and  sand. 

Limonite  is  the  usual  decomposition  product  of  iron  minerals,  re- 
sulting through  the  action  of  water,  carbon  dioxide,  humus  acid,  and 
oxygen.  It  is  hence  found  very  extensively,  and  usually  in  association 
with  such  minerals  as  pyrite,  hematite,  magnetite,  and  siderite,  and  also 
with  many  of  the  more  strictly  rock-forming  minerals  containing  iron 
in  small  quantities,  as  the  amphiboles  and  pyroxenes.  Residual  limonite 
may  be  the  result  of  the  decomposition  of  veins  containing  iron  disulphide, 
or  of  the  weathering  of  iron-bearing  rocks.  Such  limonite  is  usually 
associated  with  slates,  schists,  or  limestones.  It  occurs  extensively 


FIG.  503.— Stalactitic  limonite. 
White  Marsh,  Pennsylvania. 


FIG.  504. — Limonite  with  var- 
nish-like surface.  Salisbury,  Con- 
necticut. 


in  the  United  States  in  a  belt  extending  from  Vermont  to  Alabama, 
the  principal  mines  being  in  Alabama,  Virginia,  West  Virginia,  Ten- 
nessee, and  Georgia.  It  is  also  found  in  Texas,  Iowa,  Wisconsin,  Min- 
nesota, and  Oregon.  Very  common  as  the  yellow  coloring  matter  of 
clays  and  soils,  and  the  brownish,  rusty  stain  on  rocks. 

Constitutes  about  4  per  cent,  of  the  iron  ore  mined  in  the  United 
States.     Also  used  as  yellow  ocher,  burnt  umber,  and  sienna  in  paints. 

4.   HALOIDS 

The  following  are  the  four  most  important  halogen  minerals. 

HALITE  NaCl  Cubic 

Cerargyrite  AgCl  Cubic 

FLUORITE  CaF2  Cubic 

Cryolite  Na3AlF6  Monoclinic 

Halite  and  cerargyrite  are  isomorphous. 

HALITE   (Common  Salt,  Rock  Salt},  NaCl. 

Cubic,  hexoctahedral  class.     Crystals  are  generally  cubes,  sometimes 
in  combination  with  the  octahedron;  also  skeletal  or  hopper-shaped. 


DESCRIPTIVE  MINERALOGY  237 

Usually  in  cleavable,  fibrous,  or  granular  masses  (Fig.  505);  as  an  efflor- 
escence in  arid  regions. 

Excellent  cubical  cleavage.  Hardness  2  to  2.5.  Specific  gravity  2.1 
to  2.3.  Colorless  or  white;  when  impure  often  reddish,  blue,  gray, 
greenish,  or  black.  The  color  may  be  unevenly  distributed.  Easily 
soluble  in  water,  one  part  in  2.8  parts  of  water.  Saline  taste.  Vitreous 
luster.  Transparent  to  translucent. 

NaCl.  Sometimes  very  pure.  May  contain  varying  amounts  of  the 
chlorides  and  sulphates  of  calcium  and  magnesium,  also  admixtures 
of  gypsum,  anhydrite,  organic  matter,  clay,  and  occluded  liquids  and 
gases.  Colors  the  flame  intensely  yellow. 

Halite  occurs  very  widely  distributed.  There  are  four  methods  of 
occurrence:  (1)  Deposits,  often  of  great  thickness  and  extent;  (2)  In 
solution;  (3)  Efflorescence;  (4)  Sublimation  product. 

1 .  Deposits. — Here  salt  is  generally  associated  with  gypsum,  anhydrite, 
clay,  or  dolomite,  and  is  found  in  sedimentary  rocks  of  all  ages.  Some 


FIG.  505. — Halite.     Cleavage   cube,    Stassfurt,   Germany;   granular,    Retsof,    New   York. 

of  these  deposits  extend  over  large  areas  and  may  be  of  great  thickness. 
Thus,  the  aggregate  thickness  of  the  salt  layers  in  central  New  York  is 
over  300  feet;  near  Detroit,  Michigan,  400  feet;  Stassfurt,  Germany, 
over  1,200  feet;  Petite  Anse,  Louisiana,  over  2,000  feet. 

Many  explanations  have  been  offered  for  the  formation  of  extensive 
salt  deposits,  of  which  the  bar  theory  of  Ochsenius  is  perhaps  in  the 
larger  number  of  cases  the  most  satisfactory.  This  theory  assumes  that 
a  portion  of  the  ocean  has  been  cut  off  from  the  main  body  of  water  by  a 
bar,  which  rises  almost  to  the  surface.  Evaporation  within  this  bay 
would,  on  account  of  the  shallowness  of  the  water,  be  greatest  on  or  near 
the  bar.  This  would  cause  the  water  to  become  more  dense  and  a  por- 
tion would  settle  to  the  bottom  behind  the  bar,  causing  the  water  of  the 
bay  to  become  strongly  saline.  In  due  time  the  concentration  of  this 
saline  solution  would  be  sufficient  to  cause  the  deposition  of  the  various 
salts  in  order  of  their  solubility.  Gypsum  being  one  of  the  least  solu- 
ble is  generally  deposited  first,  followed  by  rock  salt.  As  the  evapora- 
tion continues  more  water  ^would  flow  into  the  bay  from  the  open  ocean, 
thus  furnishing  a  constant  supply.  If  the  bar  emerges  and  cuts  off  the 


238  MINERALOGY 

bay  entirely,  continued  evaporation  would  cause  the  deposition  of  not  only 
calcium  sulphate  and  rock  salt,  but  also  of  the  more  soluble  magnesium 
and  potassium  compounds,  many  of  which  are  very  complex.  The  salt 
deposits  at  Stassfurt,  Germany,  which  cover  an  area  of  about  100  square 
miles,  illustrate  the  order  in  which  deposition  will  take  place.  These 
are  underlain  by  clay  and  gypsum,  and  contain  over  thirty  different 
minerals.  Of  these  minerals,  aside  from  halite,  carnallite  (KCl.MgCl2. 
6H2O),  sylvite  (KC1),  and  kainite  (MgSO4.KC1.3H2O)  are  the  most 
important  and  in  commerce  and  industry  are  frequently  known  as  potash 
salts. 

In  the  United  States  rock  salt  has  been  mined  at  Livonia,  New  York; 
Oakwood,  near  Detroit,  Michigan;  Petite  Anse,  Louisiana;  Lyons, 
Kansas;  and  in  Sevier  County,  Utah. 

2.  In  Solution. — Common  salt  occurs  abundantly  in  solution  in  the 
ocean,  salt  lakes,  and  saline  springs  and  wells.     Most  of  the  large  quan- 
tities of  salt  produced  is  usually  obtained  by  the  evaporation  of  saline 
solutions. 

3.  Efflorescence. — Earthy  crusts  of  salt  are  frequently  found  in  arid 
regions;  thus,  in  the  steppes,  near  the  Caspian  Sea,  and  in  Africa  and 
Chile. 

4.  Sublimation  Product. — Near  volcanoes  salt  is  sometimes  found  as 
the  result  of  sublimation. 

Salt  is  used  extensively  for  household  and  dairying  purposes,  in  meat 
and  fish-packing,  in  the  manufacture  of  sodium  and  its  compounds,  in 
various  metallurgical  processes,  and  to  glaze  pottery.  Sodium  carbonate 
or  soda  ash  is  used  in  large  quantities  in  glass  and  soap  making;  sodium, 
bicarbonate  for  cooking  and  baking  and  in  medicine ;  and  sodium  cyanide 
in  the  cyanide  process  for  the  extraction  of  gold.  New  York,  Michigan, 
Ohio,  Kansas,  Louisiana,  Virginia,  California,  West  Virginia,  Texas, 
and  Utah  produce  enormous  quantities  of  salt  annually.  Of  these,  the 
first  five  furnish  about  95  per  cent,  of  the  total  production  of  the  United 
States. 

Cerargyrite  (Horn  Silver),  AgCl. 

Cubic,  hexocathedral  class.  Crystals  are  rare  and  poorly  developed. 
Generally  found  as  a  waxy  crust  or  coating,  also  stalactitic  and  dendritic. 

No  cleavage.  Highly  sectile,  cutting  easily,  and  yielding  shiny  sur- 
faces. Resembles  wax.  Very  soft.  Hardness  1  to  1.5.  Specific 
gravity,  5.5.  Pearly  gray,  yellowish,  greenish,  or  white  in  color;  on 
exposure  to  light  turns  violet,  brown,  or  black.  Transparent  to  trans- 
lucent. When  rubbed  becomes  shiny.  Waxy  or  resinous  luster. 

AgCl.  May  contain  mercury,  ferric  oxide,  or  other  impurites. 
Fuses  easily  on  charcoal  and  yields  a  globule  of  silver. 

Found  as  an  alteration  product  in  the  upper  levels  of  silver  deposits. 


DESCRIPTIVE  MINERALOGY 


239 


The  usual  associates  are  the  various  silver  minerals,  also  galena,  limonite, 
calcite,  barite,  and  cerussite.  It  has  been  observed  in  Saxony,  Norway, 
Mexico,  Peru,  Chile;  also  at  Broken  Hill,  New  South  Wales;  near 
Leadville,  Colorado;  Comstock  Lode,  Nevada;  Poor  Man's  Lode, 
Idaho;  Lake  Valley,  New  Mexico;  Cobalt,  Ontario. 
An  important  ore  of  silver. 

FLUORITE  (Fluor  Spar),  CaF2. 

Cubic,  hexoctahedral  class.     Excellent  crystals  are  common.     The 
usual    form    is    the  cube   (Fig.   506),   either  alone    or  in  combination 


FIG.  506. — Fluorite,  Cumberland.  England. 


FIG.  507. — Fluorite  (penetra- 
tion cubes).  Durham,  Weardale, 
England. 


with  the  tetrahexahedron  or  hexoctahedron.  Penetration  cubes  twinned 
according  to  the  Spinel  law  are  frequently  observed  (Fig.  507).  Also 
in  cleavable,  granular,  and  fibrous  masses. 

Excellent    octahedral    cleavage    (Fig.    508).     Hardness    4.     Specific 
gravity  3  to  3.2.     Usually  greenish,  yellowish,  or  bluish  in  color;  also 
various  shades  of  red  or  brown,  white,  and  color- 
less.     Sometimes  multicolored.     Transparent 
to    nearly    opaque.      Vitreous    luster.      Fre- 
quently strongly  fluorescent,  and  phosphores- 
cent when  heated. 

CaF2.     Usually  quite  pure. 

Fluorite  is  found  in  veins  in  limestones  and    |^^         ***i^M 
dolomites,  less  frequently  in  granitic  rocks  and 
sandstones.     It    is    also    a    common    gangue 
mineral  with  ores  or  lead,  silver,  copper,  and 
especially   tin.      The   common   associates  are        FlG-  508.— Fluorite  (octa- 

,  ,     ,      .  J  . .      . ,  i    -  hedral  cleavage) .    Near  Rosi- 

galena,  sphalerite,  cassitente,  calcite,    quartz,    ciare,  Illinois. 

barite,  pyrite,  chalcopyrite,  topaz,  tourmaline, 

and  apatite.     Excellent  crystals  occur  at  Cumberland,  Cornwall,  and 

Derbyshire,   England.     Large  quantities  are  mined  annually  in  Hardin 

County,  Illinois,  and  Crittenden  and  Livingstone  counties,  Kentucky. 


240  MINERALOGY 

Smaller  amounts  are  obtained  from  New  Hampshire,  Colorado,  Arizona, 
and  New  Mexico.  Fluorite  is  a  common  mineral  and  occurs  widely 
distributed. 

Fluorite  is  used  extensively  in  the  manufacture  of  open  hearth  steel, 
iron  and  steel  enamel  ware,  opalescent  glass,  cyanamide,  hydrofluoric 
acid,  and  in  the  electrolytic  refining  of  antimony  and  lead. 

CRYOLITE  (Ice-stone),  Na3AlF6. 

Monoclinic,  prismatic  class.  Crystals  are  cubical  in  habit.  Usually 
observed  in  compact,  granular,  or  cleavable  masses  (Fig.  509). 

Basal  and  prismatic  cleavages,  three  directions  nearly  at  right  angles. 
Uneven  fracture.  Hardness  2.5  to  3.  Specific  gravity  2.9  to  3.  Color- 
less to  snow-white,  more  rarely  reddish,  brownish,  or  black.  Pearly  luster 
on  the  basal  pinacoid,  elsewhere  vitreous  to  greasy.  Often  resembles 
snow  ice  or  paraffin.  Transparent  to  translucent. 

Na3AlF6.  Usually  quite  pure.  Fuses  easily  and  imparts  a  yellow 
color  to  the  flame. 


FIG.  509. — Cryolite  (white)  and  siderite.     Ivigtut,  Greenland. 

The  only  important  occurrence  of  cryolite  is  at  Ivigtut  on  the  southern 
coast  of  Greenland,  where  it  is  found  in  veins  in  granite,  and  is  associated 
with  siderite,  chalcopyrite,  galena,  pyrite,  fluorite,  sphalerite,  columbite, 
cassiterite,  and  molybdenite.  Found  also  at  Miask  in  the  Ural  Moun- 
tains, and  in  the  Pike's  Peak  district,  Colorado. 

Used  principally  as  a  bath  in  the  manufacture  of  aluminum  by  the 
electrolytic  process;  thus,  at  Niagara  Falls,  New  York;  also  in  opalescent 
glasses  and  enamels,  and  white  Portland  cement. 

5.  NITRATES,   CARBONATES  AND  MANGAN1TES 
(a)  Nitrate 

Soda  niter  or  Chile  saltpeter  is  the  only  nitrate  occurring  in  nature  in 
sufficient  quantities  to  warrant  a  description. 


DESCRIPTIVE  MINERALOGY 


241 


SODA  NITER  (Chile  Saltpeter),  NaNO3. 

Hexagonal,  ditrigonal  scalenohedral  class.  Crystals  resemble  those 
of  calcite,  but  are  rare.  Generally  in  crystalline  aggregates  or  grains, 
also  in  crusts  or  deposits  of  great  extent. 

Perfect  rhombohedral  cleavage.  Conchoidal  fracture.  Hardness 
1.5  to  2.  Specific  gravity  2.1  to  2.3.  Vitreous  luster.  Colorless,  white, 
yellowish,  gray,  or  reddish  brown.  Transparent  to  nearly  opaque. 
Cooling  and  saline  taste. 

NaNO3.  Usually  contains  some  sodium  chloride  and  sodium  sul- 
phate. Easily  soluble  in  water.  Absorbs  moisture.  Colors  flame 
intensely  yellow.  Mixed  with  rock  salt,  guano,  gypsum,  clay,  and  sand, 
it  occurs  in  extensive  deposits,  6  to  12  feet  thick,  in  the  deserts  of  Atacama 
and  Tarapaca  in  northern  Chile.  The  crude  material  is  called  caliche, 
and  must  contain  about  50  per  cent,  sodium  nitrate  to  be  considered  high 
grade.  Smaller  quantities  also  occur  in  San  Bernardino  and  Inyo  Coun- 
ties, California;  Humboldt  County,  Nevada;  and  in  New  Mexico. 

Soda  niter  is  a  very  important  commercial  mineral.  It  is  used 
extensively  as  a  fertilizer,  in  the  manufacture  of  nitric  and  sulphuric  acid 
and  potassium  nitrate.  It  is  also  a  source  of  iodine,  which  is  present 
in  small  amounts  as  lautarite  (Ca(IO3)2). 


(6)  Carbonates 

Some  of  the  most  widely  distributed  minerals  are  carbonates, 
of  them  are  of  great  importance  commercially. 

CALCITE  GROUP 


Several 


CaCO3  Hexagonal 

CaMg(CO3)2  Hexagonal 

MgCO3  Hexagonal 

ZnCOs  Hexagonal 

MnCO3  Hexagonal 

FeCO3  Hexagonal 

ARAGONITE  GROUP 

CaCO3  Orthorhombic 

SrCO3  Orthorhombic 

BaCO3  Orthorhombic 

PbCO3  Orthorhombic 

MALACHITE  GROUP 

CuCO3.Cu(OH)2  Monoclinic 

2CuCO.2Cu(OH)2  Monoclinic 

The  calcite  and  aragonite  groups  form  an  isodimorphous  series. 
CaCOs  is  dimorphous  with  modifications  in  the  hexagonal  and  ortho- 
rhombic  systems,  known  as  calcite  and  aragonite,  respectively. 

Calcite  Group 

This  group  contains  six  members,  of  which  calcite  is  the  most  common 
and  important.  All  of  these  minerals  possess  a  perfect  rhombohedral 
cleavage. 

16 


CALCITE 

DOLOMITE 

MAGNESITE 

SMITHSONITE 

RHODOCHROSITE 

SIDERITE 


ARAGONITE 
STRONTIANITE 
Witherite 
CERUSSITE 


MALACHITE 
AZURITE 


242 


MINERALOGY 


CALCITE  (Cakspar),  CaCO3. 

Hexagonal,  ditrigonal  scalenohedral  class.    Commonly  in  good  crystals ; 
often  very  complex.     The  habit  varies  greatly  and  may  be  obtuse  or 


FIG.  510. — Calcite    (scalenohe- 
dron).     Joplin,  Missouri. 


FIG.  511. — Calcite.     Cumberland,  England. 


acute  rhombohedral,  tabular,  long  prismatic,  or  scalenohedral  (Figs. 
510  and  511).  Over  300  forms  have  been  observed.  Twins  are  relat- 
ively common.  The  two  most  important  laws  involve  twinning  parallel 


FIG.  512.— Calcite 
(twinned  parallel  to  the 
base).  Guanajuato, 
Mexico. 


Joplin,  Missouri. 


to  (1)  the  basal  pinacoid  (Fig.  512),  and  (2)  the  negative  rhombohedron 
(  —  Y^K)  (Fig.  513).  Calcite  also  occurs  in  granular,  lamellar,  fibrous, 
compact,  porous,  orj  earthy  masses;  less  frequently  it  is  oolitic,  pisolitic, 
or  stalactitic. 


DESCRIPTIVE  MINERALOGY  243 

The  highly  perfect  rhombohedral  cleavage  (105°)  is  very  characteris- 
tic. Hardness  3.  Specific  gravity  2.72.  Vitreous  to  earthy  luster. 
Commonly  colorless,  white,  or  yellowish,  but  may  be  any  color.  Trans- 
parent to  opaque.  Transparent  varieties  show  strong  double  refraction 
(Fig.  514). 

CaCO3.  Sometimes  very  pure.  May  contain  varying  amounts  of 
magnesium,  iron,  or  manganese  replacing  the  calcium.  Often  mixed  with 
limonite,  hematite,  organic  matter,  sand,  or  clay.  JCasily  soluble  with  a 
brisk  effervescence  in  cold  dilute  acids.  This  test  serves  to  distinguish 
calcite  from  dolomite,  which  does  not  effervesce  in  cold  acid.  Calcite 
may  be  distinguished  from  aragonite  by  Meigen's  test,  which  consists  of 
boiling  the  powdered  minerals  in  a  solution  of  cobalt  nitrate.  When 


FIG.  514. — Calcite:  Variety,    Iceland    spar,    showing    double    refraction.     Big    Timbe^, 

Montana. 

calcite  is  treated  in  this  way, 'the  powder  remains  unchanged  or  turns  a 
pale  yellow,  while  aragonite  assumes  a  lilac-red  color. 

The  different  varieties  of  calcite  may  be  grouped  as  follows:  (a) 
ordinary  calcites,  (6)  limestones,  (c)  marbles,  (d)  chalk  and  marl,  and  (e) 
spring,  stream,  and  cave  deposits. 

(a)  Ordinary  Calcites. — These  include  crystals,  and  cleavable,  fibrous, 
and  lamellar  masses. 

1.  Dog-tooth  Spar. — Scalenohedral  crystals,  often  in  beautiful  aggre- 
gates (Fig.  510). 

2.  Nail-head  Spar. — Prismatic   crystals   with   obtuse   rhombohedral 
terminations  (Fig.  511). 

3.  Iceland  Spar. — Colorless  and  transparent,  showing  strong  double 
refraction  (Fig.  514). 

4.  Satin  Spar. — A  fibrous  variety  with  a  silky  luster.     This  term  is 
also  applied  to  fibrous  gypsum,  pages  264  and  265. 

(6)  Limestones. — Calcite  is  the  chief  constituent  of  the  limestone 
rocks,  which  occur  so  widely  distributed.  They  are  massive,  and  may 


244  MINERALOGY 

be  dull  and  compact,  coarse  or  fine  granular,  or  composed  of  fragmental 
material. 

1.  Compact  Limestones. — These  may  be  nearly  white,  yellow,  bluish 
gray,  reddish,  or  black  in  color. 

2.  Magnesian    or    Dolomitic   Limestones. — As    the    name    indicates, 
these  limestones  contain  varying  percentages  of  magnesium  carbonate. 

3.  Lithographic   Limestones. — An    even-grained,  compact    limestone, 
suitable  for   lithographic   purposes.     That  from   Solenhofen,   Bavaria, 
is  buff  or  drab  in  color. 

4.  Hydraulic  Limestones.— These  are  impure  limestones,  containing 
from  10  to  40  per  cent,  of  clayey  impurities.     They  are  used  extensively 
in  the  manufacture  of  cement. 

5.  Bituminous  Limestones. — Owing  to  the  presence  of  much  organic 
matter,  these  limestones  yield  the  characteristic  odor  of  bitumen  when 

struck  a  blow  with  a  hammer. 

6.  Coquina. — This  is  a  mass  of  shell  re- 
mains (Fig.  515).     Found  along  the  coast 
of  Florida,  near  St.  Augustine. 

7.  Oolitic  Limestones. — These   are   com- 
posed of  small,   spherical   concretions,    re- 
sembling fish-roe. 

8.  Pisolitic     Limestones. — The      concre- 
tions  are   larger,  and   about  the  size  of  a 
pea. 

(c)  Marbles. — These   possess   a   fine   to 

FIG.  515. — Calcite:  Variety,    coarse  crystalline  structure,  and  are  meta- 
Anastatia   Island'    morphosed  limestones  (Fig.  516).     Commer- 
cially, however,  any  calcareous  rock  capable 

of  taking  a  polish  and  suitable  for  decorative  and  structural  purposes  is 
termed  a  marble. 

(d)  Chalk  and  Marl. — These  are  soft  earthy  varieties. 

1.  Chalk. — Soft,   white  or  grayish,   earthy  masses,   consisting  prin- 
cipally of  the  remains  of  foraminifera.     Found  in  large  deposits  at  Dover, 
England. 

2.  Marl. — A   soft,    calcareous   deposit   mixed   with   clay   and   sand. 
Often  contains  shell  or  organic  remains.     It  is  used  in  the  manufacture 
of  cement. 

(e)  Spring,  Stream,  and  Cave  Deposits. — These  are  due  largely  to 
the  escape  of  carbon  dioxide,  which  causes  the  soluble  calcium  bicar- 
bonate, CaH2(CO3)2,  to  pass  over  to  the  more  insoluble  normal  carbonate, 
CaCO3,  and  be  deposited.     It  is  thought  that  certain  algae  aid  in  this 
process. 

1.  Travertine,  Calcareous  Sinter ,  or  Calc  Tufa. — These  occur  around 
springs  and  in  stream  beds,  and  are  usually  porous  and  often  contain 
twigs,  leaves,  and  other  organic  remains. 


DESCRIPTIVE  MINERALOGY 


245 


2.  Stalactites. — Icicle-like  forms  suspended  from  the  roofs  of  caves. 

3.  Stalagmites. — Deposits  on  the  floors  of  caves,  usually  conical  in 
shape. 

4.  Onyx   Marble. — Compact   deposits   with   a   crystalline  structure, 
often   banded,   translucent,  and  of  colors  suitable  for  decorative  pur- 
poses (Fig.  517). 

Calcite  occurs  very  widely  distributed.  As  limestone,  marble,  chalk, 
and  marl  it  is  found  in  large  deposits,  often  of  great  thickness  and  ex- 
tending over  wide  areas.  It  is  also  abundant  .as  deposits  around  springs 
and  in  streams,  and  in  cracks  and  cavities  in  igneous  and  sedimentary 
rocks.  Often  observed  as  an  associate  of  metalliferous  ore  deposits. 
Excellent  crystals  are  very  common.  A  few  of 
the  most  noted  localities  are:  Eskifiord,  Iceland; 
Derbyshire,  Cumberland,  Devonshire,  Durham, 
Lancashire,  England;  Andreasberg,  Germany; 
Kapnik,  Hungary;  Guanajuato,  Mexico;  Joplin, 


FIG.  516. — Marble.     Near  Tate,  Georgia. 


FIG.  517. — Calcite:  Va- 
riety, Mexican  onyx.  Lehi 
City,  Utah. 


Missouri;  Rossie,  St.  Lawrence  County,  New  York;  Lake  Superior  copper 
district.  Large  and  commercially  important  deposits  of  marble  occur 
in  Vermont,  New  York,  Tennessee,  Georgia,  Maryland,  and  Colorado. 
The  different  varieties  of  calcite  are  commercially  of  great  value. 
Iceland  spar  is  used  in  optical  instruments;  limestone  for  building  pur- 
poses, quicklime,  cement,  flux  in  various  metallurgical  processes,  railroad 
ballast,  macadam,  in  lithography,  and  concrete;  marble  for  building, 
ornamental,  monumental,  and  statuary  purposes',  and  as  a  source  of 
carbon  dioxide;  chalk  for  whiting,  crayon,  scouring  and  polishing  pre- 
parations, and  as  an  adulterant;  marl  for  cement. 

DOLOMITE  (Pearl  Spar),  CaMg(CO3)2. 

Hexagonal,  trigonal  rhombohedral  class.  Rhombohedral  crystals 
are  common.  The  faces  are  frequently  curved  forming  saddle-shaped 
crystals  (Fig.  518).  Also  in  fine  to  coarse  grained,  cleavable,  or  compact 
masses. 

Perfect  rhombohedral  cleavage.  Hardness  3.5  to  4.  Specific 
gravity  2.9.  White,  reddish,  yellow,  brown,  or  black;  rarely  colorless. 
Vitreous  to  pearly  luster.  Transparent  to  translucent. 


246  MINERALOGY 

CaMg(C03)2. — In  the  crystals  of  dolomite  the  carbonates  of  calcium 
and  magnesium  are  usually  present  in  the  proportion  of  1  :  1 ;  in  massive 
varieties  this  ratio  varies  greatly,  but  CaCO3  generally  predominates. 
In  many  instances  dolomite  is  believed  to  have  been  formed  by  the  action 
of  soluble  magnesium  salts  upon  calcium  carbonate,  either  before  or  after 
emergence  from  the  sea. 

2CaC03  +  MgCl2  =  CaMg(C03)2  -f  CaCl2 

Fragments  of  dolomite  are  but  slightly  acted  upon  by  cold  dilute  acid; 
the  powder  effervesces  briskly  with  hot  dilute  acids. 


FIG.  518. — Dolomite.     Joplin,  Missouri. 

Dolomite  occurs  abundantly  in  many  ore  deposits,  and  in  cavities  of 
various  igneous  and  sedimentary  rocks.  Thus,  at  Joplin,  Missouri; 
Lockport,  New  York;  Austria;  Switzerland;  Freiberg,  Saxony.  The 
compact  granular  variety  occurs  in  deposits  of  great  thickness  and  extent. 
Thus,  some  of  the  mountain  ranges  of  central  Europe  are  principally 
dolomite.  These  crystalline  dolomites  grade  into  dolomitic  and  magne- 
sian  limestones,  see  page  244. 

Dolomite  is  used  for  building,  statuary,  monumental,  and  ornamental 
purposes;  as  a  source  of  magnesium  compounds;  and  as  refractory 
material. 

MAGNESITE,  MgCO3. 

Hexagonal,  ditrigQnal  scalenohedral  class.  Rarely  in  rhombohedral 
crystals;  usually  in  granular,  compact,  or  earthy  masses  resembling 
unglazed  porcelain  (Fig.  519).  Also  coarsely  crystalline  resembling 
coarse  dolomite  or  marble  in  texture. 

Crystals  have  a  rhombohedral  cleavage.  Conchoidal  fracture  is 
conspicuous  on  massive  varieties.  Brittle.  Hardness  3.5  to  4.5.  Speci- 
fic gravity  2.9  to  3.1.  Colorless,  white,  yellow,  brown,  or  blackish. 
Vitreous  to  dull  luster.  Transparent  to  opaque. 

MgC03.  Iron  or  calcium  may  be  present.  Powdered  magnesite  is 
soluble  in  hot  dilute  acids. 

Magnesite  is  commonly  the  result  of  the  hydra tion  and  carbonatization 
of  magnesium.  Thus,  olivine,  (Mg,Fe)2SiO4,  may  alter  to  magnesite, 


DESCRIPTIVE  MINERALOGY  247 

serpentine,  limonite,  and  opal.  It  is  found  in  veins  in  talcose  and  chlo- 
ritic  schists  and  in  serpentine.  It  occurs  in  Moravia  and  Styria,  Austria; 
Silesia;  Zillerthal,  Tyrol;  Greece;  and  very  extensively  in  Santa  Clara, 
Sonoma,  Napa,  Kern,  Fresno,  and  San  Benito  counties,  California,  and  in 
Stevens  County,  Washington. 


FIG.    519. — Magnesite.        Tulare          FIG.  520. — Smithsonite  (pseudomorph  after 
County,  California.  calcite).     Mineral  Point,  Wisconsin. 

Magnesite  is  used  chiefly  in  the  manufacture  of  refractory  bricks, 
crucibles,  furnace  hearths,  oxychloride  or  Sorel  cement,  and  magnesium 
sulphite  for  the  digestion  and  whitening  of  wood-pulp  paper;  as  a  source 
of  carbon  dioxide  and  magnesium  compounds;  when  mixed  with  asbestos 
it  serves  as  a  boiler  and  steam-pipe  covering. 

SMITHSONITE  (Calamine,  Dry  Bone),  ZnCO3. 

Hexagonal,  ditrigonal  scalenohedral  class.  Crystals  are  usually 
small,  and  rough  or  curved.  Generally  found  in  reniform,  botryoidal, 
stalactitic,  or  compact  granular  masses.  Dry  bone  is  a  term  given  to 
cellular  and  porous  varieties. 

Rhombohedral  cleavage,  observed  on  crystals.  Uneven  to  splintery 
fracture.  Hardness  5.  Specific  gravity  4.1  to  4.5.  Color  is  commonly 
gray  or  .brown;  also  white,  yellow,  blue,  green,  and  pink.  Translucent 
to  opaque.  Vitreous  to  pearly  luster. 

ZnCO3.  Iron,  manganese,  calcium,  and  magnesium  may  be  present. 
Turkey  fat  is  yellow  smithsonite  containing  greenockite,  CdS.  Common 
as  a  pseudomorph  after  calcite,  especially,  at  Mineral  Point,  Wisconsin 
(Fig.  520). 

Smithsonite  is  a  secondary  mineral  and  occurs  extensively  in  the  upper 
levels  in  limestones  and  dolomites.  It  is  often  the  result  of  the  action  of 
carbonated  waters  on  other  zinc  minerals.  The  common  associates  are 
sphalerite,  hemimorphite,  galena,  limonite,  and  calcite.  Sometimes  it  is 
mixed  with  sand  and  clay.  Occurs  at  Broken  Hill,  New  South  Wales; 


248 


MINERALOGY 


Laurium,  Greece;  Hungary;  Scotland;  Kelly,  New  Mexico;  also  exten- 
sively in  Missouri,  Arkansas,  Iowa,  Wisconsin,  and  Virginia,  where  it  is 
mined  as  zinc  ore.  The  term  calamine  is  sometimes  applied  to  smithson- 
ite,  but  it  refers  more  properly  to  hemimorphite,  H2Zn2Si05,  page  280. 
These  two  minerals  often  occur  in  intimate  association. 

Chiefly  used  as  an  ore  of  zinc;  green,  blue,  and  yellowish  varieties  are 
sometimes  polished  for  gem  and  ornamental  purposes'. 

RHODOCHROSITE,  MnCO3. 

Hexagonal,  ditrigonal,  scalenohedral  class.  Crystals  are  rhombohedral 
in  habit,  small,  and  quite  rare  (Fig.  521).  Generally  in  cleavable, 
granular,  and  botryoidal  masses;  also  in  crusts. 

Perfect  rhombohedral  cleavage.  Uneven  fracture.  Hardness  3.5 
to  4.5.  Specific  gravity  3.3  to  3.6.  Usually  rose-red  or  pink  in  color; 
also  gray,  dark  brown,  and  more  rarely  colorless.  Vitreous  to  pearly 
luster.  Translucent. 


FIG.  521. — Rhodochrosite  (Rhom- 
bohedrons).    Lake  County,  Colorado. 


FIG.  522. — Siderite  (dark)  with  dolomite. 
Salzburg,  Austria. 


MnCO3.  Calcium,  iron,  zinc,  and  magnesium  are  often  present 
replacing  the  manganese.  Occurs  as  a  pseudomorph  after  calcite  and 
fluorite. 

Usually  found  with  iron,  lead,  gold,  silver,  copper  ores;  and  other 
manganese  minerals.  Most  common  associates  are  galena,  sphalerite, 
pyrite,  rhodonite,  and  psilomelane;  thus,  at  Hucha,  Spain;  Freiberg, 
Saxony;  Kapnik,  Hungary;  Franklin  Furnace,  New  Jersey;  Alicante, 
Colorado;  Butte,  Montana;  Austin,  Nevada. 

Rhodochrosite  is  not  a  very  common  mineral.  It  is  sometimes  used 
as  a  source  of  manganese  and  its  compounds. 

SIDERITE,  (Spathic  Iron,  Chalybite)  FeCO3. 

Hexagonal,  ditrigonal  scalenohedral  class.  Distorted  and  curved 
rhombohedral  crystals  (saddle-shaped)  are  quite  common  (Fig.  522). 
Usually  found  in  cleavable,  granular,  botryoidal,  or  fibrous  masses. 

Perfect  rhombohedral  cleavage.  Conchoidal  fracture.  Hardness 
3,5  to  4.5.  Specific  gravity  3.7  to  3.9.  Vitreous  to  pearly  luster.  Usually 
brownish  to  nearly  black  in  color;  also  gray,  green,  and  white.  Trans- 
lucent to  nearly  opaque.  Streak  white  or  yellowish. 


DESCRIPTIVE  MINERALOGY  249 

FcCO3.  Usually  contains  some  CaCO3  and  MnCO3.  Manganiferous 
varieties  are  termed  oligonite.  When  mixed  with  clay,  sand,  and  organic 
matter,  it  is  often  called  clay  ironstone  or  blackband.  Occurs  as  a  pseudo- 
morph  after  calcite,  aragonite,  dolomite,  barite,  and  fluorite.  It  alters  to 
limonite,  hematite,  and  magnetite. 

Siderite  occurs  -commonly  with  sulphide  ore  deposits,  also  in  beds  and 
as  concretions  in  limestones  and  shales.  The  common  associates  are 
pyrite,  chalcopyrite,  galena,  tetrahedrite,  and  cryolite.  It  occurs  with 
ore  deposits  in  the  Hartz  Mountains;  Pribram,  Bohemia;  Cornwall, 
England;,  Freiberg,  Saxony;  with  cryolite  and  chalcopyrite  in  southern 
Greenland;  in  beds  and  as  concretions  in  Westphalia;  southern  Wales; 
Silesia;  Roxbury,  Connecticut;  St.  Lawrence  County,  New  York;  in  the 
coal  measures  in  eastern  Ohio,  Kentucky,  and  western  Pennsylvania. 

A  minor  ore  of  iron.  If  it  contains  considerable  manganese,  it  is 
used  for  spiegeleisen.  '9 

Aragonite  Group 

The  members  of  this  group  crystallize  in  the  orthorhombic  system. 
The  prism  angle  of  these  minerals  approximates  120°,  so  that  crystals 
frequently  have  a  pseudohexagonal  development. 

ARAGONITE,  CaCO2. 

Orthorhombic,  bipyramidal  class.  Crystals  are  quite  common 
and  show  great  diversity  in  development.  They  may  be  (1)  domatic  or 


FIG.  523. — Aragonite  (trillings).  FIG.    524. — Aragonite:  Variety,  flos  ferri. 

Girgenti,  Sicily.  Styria,  Austria. 

chisel-like,  (2)  acute  pyramidal  or  spear-shaped,  and  (3)  prismatic  and 
pseudohexagonal,  consisting  of  a  prism  and  striated  base.  The  prism 
angle  is  116°  16'.  This  pseudohexagonal  symmetry  is  often  accentuated 
by  twinning  parallel  to  a  face  of  the  unit  prism  (Fig.  523).  Contact, 
cyclic,  and  penetration  twins  are  common.  Also  occurs  in  radial, 
branching,  columnar,  and  fibrous  aggregates;  oolitic,  globular,  stalactitic, 
and  in  crusts. 


250  MINERALOGY 

Imperfect  brachypinacoidal  and  prismatic  cleavages.  Conchoidal 
fracture.  Hardness  3.5  to  4.  Specific  gravity  2.9  to  3.  Most  commonly 
colorless,  white,  or  yellow;  also  reddish,  bluish,  or  black.  Greasy  luster 
on  fracture  surfaces,  elsewhere  vitreous.  Transparent  to  translucent. 
CaCOs.  May  contain  some  strontium.  Effervesces  -easily  with 
acids,  but  not  as  easily  as  calcite.  Massive  varieties  are  easily  dis- 
tinguished from  calcite  by  Meigen's  test,  see  page  169.  Occurs  as  a 
pseudomorph  after  gypsum  and  calcite,  but  calcite  pseudomorphs  after 
aragonite  are  more  abundant.  At  about  470°C.,  aragonite  changes  to 
calcite.  Aragonite  is  usually  deposited  from  hot  solutions  while  calcite 
is  formed  from  cold  solutions.  It  may  also  be  formed  at  ordinary 
temperatures  through  the  action  of  organic  agencies,  or  by  precipitation 
from  saline  waters  containing  sulphates. 

Aragonite  is  found  (1)  in  cracks  and  cavities,  often  associated  with 
the  zeolites.  (2)  In  ore  deposits,  especially  iron  ore.  The  coralloidal 
variety  occurring  with  siderite  at  Htittenberg, 
Carinthia,  is  termed  flos  ferri  (Fig.  524).  (3) 
Disseminated  in  clay,  associated  with  gypsum, 
sulphur,  and  celestite.  (4)  As  a  deposit  from 
hot  springs  and  geysers,  sometimes  pisolitic  and 
in  crusts.  (5)  It  constitutes  the  pearly  layer 
of  many  shells  and  pearls.  Aragonite  is  not 
nearly  as  common  as  calcite.  Excellent  crystals 
are  found  at  Herrengrund,  Hungary;  Bilin, 
Karlsbad,  and  Horschenz,  Bohemia;  Aragon, 
Spain;  Girgenti,  Sicily;  Alton  Moor,  England; 
other  varieties  at  Hoboken,  New  Jersey;  Lock- 
port,  New  York;  Warsaw,  Illinois;  Organ  Moun- 

PIG.    525.-Strontianite.     tains    New  Mexico. 
Dreistemfurt,     Westphalia,  . 

Germany.  Aragonite  is  of  no  importance  commercially. 

STRONTIANITE,  SrCO3. 

Orthorhombic,  bipyramidal  class.  Crystals  are  usually  spear- 
shaped  or  acicular  and  arranged  in  radial  aggregates.  Forms  and  twin- 
ning are  similar  to  those  of  aragonite.  Pseudohexagonal  with  a  prism 
angle  of  117°  19'.  Also  granular  and  compact,  sometimes  with  a  radial 
fibrous  structure  (Fig.  525). 

Imperfect  prismatic  cleavage.  Conchoidal  fracture.  Hardness  3.5 
to  4.  Specific  gravity  3.6  to  3.8.  Colorless,  white,  gray,  yellow,  and 
green.  Vitreous  luster,  greasy  on  fracture  surfaces.  Transparent  to 
translucent. 

SrCO3.  Usually  contains  some  calcium  and  barium.  Occurs  as  a 
pseudomorph  after  celestite. 

Occurs  in  ore  deposits,  commonly  with  barite  and  galena.  Important 
localities  are:  Strontian,  in  Argyllshire,  Scotland;  Hamm  in  Westphalia, 


DESCRIPTIVE  MINERALOGY 


251 


Germany;  Schoharie,  New  York;  Ida,  Michigan;  near  Austin,  Texas; 
Skagit  County,  Washington. 

Strontianite  is  a  source  of  strontium  compounds,  some  of  which  are 
used  extensively.  The  oxide  and  hydroxide  are  of  importance  in  the 
precipitation  of  sugar  from  molasses ;  the  nitrate,  carbonate,  and  oxalate 
are  used  for  red  fire;  and  the  iodide, 'bromide,  and  lactate  in  medicine. 

Witherite,  BaCO3. 

Orthorhombic,  bipyramidal  class.  Usually  in  pseudohexagonal 
bipyramids,  resembling  quartz  (Fig.  526).  These  are  penetration 
trillings  with  the  twinning  plane  parallel  to  the  unit  prism.  The  prism 
angle  is  117°  48'.  Parallel  groups  not  uncommon.  Also  in  compact, 
botryoidal,  reniform,  or  globular  masses;  some- 
times with  a  lamellar  or  radial  fibrous  structure. 

Imperfect  prismatic  cleavage.  Uneven  fracture. 
Hardness  3.5.  Specific  gravity  4.2  to  4.35.  Color- 
less, grayish,  white,  or  yellowish.  Vitreous  luster, 
on  fracture  surfaces  somewhat  greasy.  Translu- 
cent to  transparent. 

BaCO3.     Usually  quite  pure. 

Occurs  with  deposits  of  galena  in  northwestern 
England;  thus,  at  Fallowfield,  Northumberland; 
Durfton,  Westmoreland;  Alston  Moor,  Cumber- 
land; with  barite  at  Freiberg,  Saxony;  Lexington, 
Kentucky;  Thunder  Bay  district,  Lake  Superior. 

Witherite  is  used  to  adulterate  white  lead  and 
in  the  extracting  of  sugar  from  sugar-beets. 


FIG.  526. — Witherite 
(trillings) .  Northum- 
berland, England. 


CERUSSITE  (White  Lead  Ore),  PbCO3. 

Orthorhombic,  bipyramidal  class.  Crystals  are  generally  tabular, 
prismatic,  or  pyramidal  in  habit;  frequently 
arranged  in  clusters  or  star-shaped  groups. 
Often  very  complex.  Pronounced  pseudo- 
hexagonal  symmetry,  the  prism  angle  being 
117°  14'.  Twins  are  very  common  and 
similar  to  those  of  aragonite.  Also  in  gran- 
ular, fibrous,  and  compact  masses,  interlaced 
bundles  (Fig.  527)  and  stalactitic. 

Hardness  3  to  3.5.  Specific  gravity  6.4 
to  6.6.  Generally  colorless,  white,  or  gray. 
Adamantine  luster,  sometimes  silky.  Trans- 
parent to  almost  opaque. 

PbCO3.     At   times    contains   some   silver 
and  zinc.     Occurs  as  a  pseudomorph  after  galena  and  anglesite. 

Found  usually  in  the  upper  levels  of  galena  deposits,  from  which  it 


FIG.  527. — Cerussite. 
ville,  Colorado. 


Lead- 


252 


MINERALOGY 


has  resulted  by  the  action  of  carbonated  waters.  Common  associates 
are  galena,  pyromorphite,  anglesite,  malachite,  and  limonite.  Occurs  at 
Broken  Hill,  New  South  Wales;  Leadhills,  Scotland;  various  places  in 
Mexico;  Leadville,  Colorado;  Pima  and  Yuma  counties,  Arizona;  Park 
City,  Utah;  Coeur  d'Alene  district,  Idaho. 
An  important  ore  of  lead  and  silver. 

MALACHITE  GROUP 

This  group  includes  two  basic  carbonates  of  copper,  which  are  of 
great  importance  commercially. 

MALACHITE  (Green  Carbonate  of  Copper],  CuCO3.Cu(OH)2. 

Monoclinic,  prismatic  class.  Crystals  are  usually  acicular,  very 
slender,  and  without  good  terminations;  often  arranged  in  groups  or 
tufts.  Commonly  in  reniform,  botryoidal,  and  stalactitic  masses  with 
smooth  surfaces  and  a  banded  or  radial  fibrous  structure  (Fig.  528); 
also  earthy  and  in  velvety  crusts. 

Conchoidal  to  splintery  fracture.  Hardness  3.5  to  4.  Specific 
gravity  3.7.  to  4.1.  Bright  emerald  green,  grass  green,  to  nearly  black  in 

color.  Translucent  to  opaque.  Silky, 
adamantine,  or  dull  luster.  Light  green 
streak. 

CuCO3.Cu(OH)2.  Masses  may  con- 
tain the  oxides  of  iron  and  manganese, 
clay,  and  sand.  Occurs  commonly  as  a 
pseudomorph  after  cuprite,  azurite,  and 
native  copper. 

Malachite  is  a  common  alteration  pro- 
duct of  copper  minerals,  resulting  from 
the  action  of  carbonated  waters,  and 
hence,  is  found  in  smaller  or  larger  quan- 
tities in  the  upper  levels  of  all  copper  mines.  Common  associates 
are  azurite,  cuprite,  native  copper,  chalcocite,  chalcopyrite,  and  bornite. 
Occurs  in  Targe  quantities  in  the  Ural  Mountains;  at  Chessy,  France, 
as  pseudomorphs  after  cuprite;  Cornwall,  England;  Rhodesia;  Chile; 
Bisbee  and  Clifton  districts,  Arizona;  Park  City,  Utah;  as  a  coating  on 
native  copper  in  the  Lake  Superior  copper  district. 

An  important  ore  of  copper,  especially  in  Arizona.  Also  used  in 
jewelry  and  for  ornamental  purposes,  such  as  table  tops  and  vases. 
Malachite  matrix  is  a  term  given  to  polished  specimens  with  admixtures 
of  gangue  material. 

AZURITE  (Chessylite,  Blue  Carbonate  of  Copper),  2CuCO3.Cu(OH)2. 

Monoclinic,  prismatic  class.  Short  prismatic  or  tabular  crystals, 
often  very  complex,  and  arranged  in  spherical  aggregates.  Commonly 


FIG.  528.— Malachite   (polished). 
Rhodesia,  Africa. 


DESCRIPTIVE  MINERALOGY 


253 


found  in  reniform  or  botryoidal  masses,  with  a  velvety,  radial  fibrous 
structure;  also  earthy  and  in  crusts. 

Hardness  3.5.  .  Specific  gravity  3.7  to  3.8.  Vitreous  to  adamantine 
luster.  Light  azure  to  deep  blue  in  color.  Streak  light  blue.  Trans- 
lucent to  opaque. 

2CuC03.Cu(OH)2.  Occurs  as  a .  pseudomorph  after  cuprite  and 
tetrahedrite.  Alters  to  malachite. 

Origin  and  occurrences  are  the  same  as  for  malachite;  not  as 
common  as  malachite.  Excellent  crystals  occur  at  Chessy,  France; 
Ural  Mountains;  Chile;  Bisbee  and  Clifton  copper  districts,  Arizona;  also 
in  Utah  and  California. 

Used  as  an  ore  of  copper.  When  intimately  mixed  with  malachite,  it 
is  sometimes  polished  for  gem  purposes  and  sold  as  azur malachite. 

(c)  MANGANITES 

These  minerals  contain  large  percentages  of  manganese,  but  the 
conposition  of  only  one,  hausmannite,  is  sufficiently  constant  to  warrant 
the  assigning  of  a  chemical  formula. 


Hausmannite 
Psilomelane 


Tetragonal 
Amorphous 


Mn2MnO4 

MnO2,  BaO,  H2O,etc. 


K 


Of  these  minerals  psilomelane  is  the  more  common  and  important. 

Hausmannite,  Mn2MnO4. 

Tetragonal,  scalenohedral  class.  Crys- 
tals are  acute  pyramidal  and  often  form 
cyclic  twins.  Found  generally  in  granular 
to  compact  masses. 

Perfect  basal  cleavage.  Hardness  5  to 
5.5.  Specific  gravity  4.7  to  4.8.  Brownish 
black  to  black  in  color.  Chestnut  brown 
streak.  Greasy  metallic  luster.  Opaque. 

Mn2MnO4.  Soluble  in  hydrochloric  acid 
with  an  evolution  of  chlorine. 

A  comparatively  rare  mineral.  The 
common  associates  are  pyrolusite,  psilo- 
melane, magnetite,  barite,  and  hematite. 
Occurs  at  Ilfeld  and  Ilmenau,  Germany; 
Pajsberg  and  Langban,  Sweden. 

Psilomelane  (Black  Hematite},  MnO2,  BaO,  H2O,  K20,  etc. 

Occurs  only  in  botryoidal,  reniform,  or  stalactitic  masses,  usually 
having  smooth  surfaces  (Fig.  529). 

Hardness  5  to  6,  but  may  be  soft  superficially,  due  to  a  coating  of 
pyrolusite.  Specific  gravity  3.7  to  4.7.  Dark  gray  to  iron  black  in 
color.  Brownish  black  streak.  Dull  or  submetallic  luster.  Opaque. 


FIG.  529. — Psilomelane.     Iron- 
wood,  Michigan. 


254 


MINERALOGY 


The  composition  varies  greatly;  MnO2,  70  to  90  per  cent.;  BaO,  6  to 
17  per  cent.;  H2O,  1  to  6  per  cent.  It  may  also  contain  potassium, 
calcium,  copper,  and  silicon.  Evolves  chlorine  when  treated  with 
hydrochloric  acid. 

Psilomelane  is  a  secondary  mineral,  and  is  always  associated  with  other 
manganese  minerals,  limonite,  or  barite.  Found  at  Ilfeld  and  Ilmenau, 
Germany;  Cornwall,  England;  Brandon,  Vermont;  Batesville,  Arkansas; 
Blue  Ridge  region,  Virginia;  Cartersville,  Georgia. 

One  of  the  important  ores  of  manganese. 

6.  SULPHATES,  CHROMATES,  MOLYBDATES,  TUNGSTATES,  AND 

URANATES 

The  minerals  belonging  to  this  division  may  be  conveniently  arranged 
in  the  following  groups: 

BARITE  GROUP 


ANHYDRITE 
CELESTITE 
BARITE 
ANGLESITE 

Crocoite 


Wulfenite 

Scheelite 

Huebnerite 

WOLFRAMITE 

Ferberite 

Uraninite 

ALUNITE 

Brochantite 

GYPSUM 

Epsomite 

Melanterite 

Chalcanthite 


CaS04 
SrSO4 
BaS04 
PbS04 


PbCrO4 

WOLFRAMITE  GROUP 

PbMoO4 

CaW04 

MnW04 

(Fe,Mn)WO4 

FeW04 

UO3.UO2,PbO,etc. 

K2(A1.20H)6(S04)4 

CuSO4.3Cu(OH)2 

CaS04.2H2O 

MgS04.7H20 

FeSO4.7H2O 

CuS04.6H20 


Orthorhombic 
Orthorhombic 
Orthorhombic 
Orthorhombic 

Monoclinic 


Tetragonal 
Tetragonal 
Monoclinic 
Monoclinic 
Monoclinic 

Cubic 

Hexagonal 

Orthorhombic 

Monoclinic 

Orthorhombic 

Monoclinic 

Triclinic 


Most  of  these  minerals  possess  non-metallic  lusters. 


Barite  Group 

This  group  may  be  subdivided  into  two  series.  One  of  these  series 
has  Orthorhombic  crystallization,  the  other  monoclinic.  Crocoite  is 
the  only  representative  of  the  second  series. 

ANHYDRITE,  CaSO4. 

Orthorhombic,  bipyramidal  class.  Crystals  are  prismatic  or  thick 
tabular  in  habit,  but  not  common.  Generally  in  granular,  cleavable, 


DESCRIPTIVE  MINERALOGY 


255 


fibrous,  or  contorted  masses.  When  granular  may  resemble  marble  or 
lumps  of  sugar  (^Fig.  530). 

Pinacoidai  cleavages  in  three  directions  at  right  angles,  yielding  cubic 
or  rectangular  fragments.  Conchoidal  fracture.  Hardness  3  to  3.5. 
Specific  gravity  2.7  to  3.  Colorless,  white,  grayish,  bluish,  reddish,  or 
black.  Vitreous  to  pearly  luster.  Transparent  to  translucent. 

CaSO4.  Often  mixed  with  organic 
matter.  Absorbs  water  and  alters  to 
gypsum,  CaSO4.2H2O,  causing  an  increase 
of  33  to  62  per  cent,  of  the  original 
volume.  This  hydration  is,  no  doubt, 
the  cause  of  the  many  local  disturbances 
in  the  rock  strata  commonly  observed  in 
regions  where  gypsum  occurs;  thus,  in 
central  New  York,  and  the  Island  of  Put- 
in-Bay in  Lake  Erie.  Occurs  sometimes 
as  a  pseudomorph  after  gypsum. 

Found  commonly  in  limestones  and 
shales  associated  with  halite  and  gypsum. 

Some  of  the  principal  localities  are:  the  Stassfurt  salt  district,  Germany; 
Hall,  Tyrol;  Bex,  Switzerland;  Nova  Scotia;  New  Brunswick;  Lockport, 
New  York;  Detroit,  Michigan;  Ellsworth  County,  Kansas. 

Anhydrite  is  of  little  use  commercially.  A  silicious  variety  is  some- 
times cut  and  polished  for  ornamental  purposes. 


FIG.  530. — Anhydrite.     Oakwood 
Salt  Shaft,  Detroit,  Michigan. 


FIG.  531.  FIG.  532.  FIG.     533.— Celestite 

(Tabular).  Woolmith 
Quarry,  Monroe  County, 
Michigan. 

CELESTITE,   SrSO4. 

Orthorhombic,  bipyramidal  class.  Tabular  or  prismatic  crystals 
are  common  (Figs.  531,  532,  and  533).  Also  in  cleavable,  granular, 
or  fibrous  masses. 

Perfect  basal  and  prismatic  cleavages.  Uneven  fracture.  Hardness 
3  to  3.5.  Specific  gravity  3.9  to  4.  Vitreous  to  pearly  luster.  Generally 


256  MINERALOGY 

possesses  a  faint  blue  tinge,  but  may  be  white,  yellow,  and  more  rarely 
green  or  reddish.  Transparent  to  translucent. 

SrSO4.  Usually  very  pure,  but  may  contain  small  amounts  of  calcium 
and  barium.  Imparts  a  red  color  to  the  flame.  More  soluble  in  water 
than  barite. 

Celestite  is  usually  associated  with  sulphur,  gypsum,  halite,  aragonite, 
and  occasionally  galena  and  sphalerite.  There  are  two  principal  types 
of  occurrences: 

(1)  Disseminated  as  crystals  or  irregular  particles  in  shales,  limestones, 
and  dolomites.     By  the  action  of  circulating  water  the  celestite  is  dis- 
solved and  these  rocks  become  more  or  less  porous.     They  are  often 
called  gashed,  acicular,  or  vermicular  limestones  and  dolomites.     Such 
rocks  occur  near  Syracuse,  N.  Y.,  and  at  various  places  in  Michigan  and 
northern  Ohio. 

(2)  In  cracks  and  cavities  in  rocks  of  varying  ages  but  principally 
of  sedimentary  origin.     Most  of  the  best  known  localities  for  the  occur- 
rence of  celestite  are  of  this  type.     It  is  found  in  association  with  sul- 
phur, gypsum,  and  aragonite  in  the  Girgenti  sulphur  district  of  Sicily; 
also  at  Maybee,  Michigan;  with  halite  at  Bex,  Switzerland;  excellent 
crystals,  some  over  18  inches  in  length  are  found  on  the  Island  of  Put- 
in-Bay, Lake  Erie;  Mineral  County,  West  Virginia;  Kingston,  Canada; 
San   Bernardino    County,    California;    Burnet    County,   Texas;   Brown 
County,  Kansas. 

Used  in    the  manufacture  of  strontium  compounds. 

BARITE  (Heavy  Spar,  Barytes),  BaSO4. 

Orthorhombic,  bipyramidal  class.  Tabular  and  prismatic  crystals 
are  very  common,  usually  well  developed  (Figs.  534  to  539) ;  often  com- 


FIG.  534.  FIG.  535.  FIG.  536.  FIG.    537. 

plex.  Tabular  crystals  may  be  arranged  in  crested  divergent  groups 
(Fig.  540).  Also  in  cleavable,  granular,  fibrous,  or  reniform  masses; 
sometimes  lamellar,  nodular,  or  earthy. 

Perfect  basal  and  prismatic  cleavages.  Uneven  fracture.  Hardness 
2.5  to  3.5.  Specific  gravity  4.3  to  4.7.  Colorless,  white,  yellow,  blue, 
brown,  or  red.  Transparent  to  opaque.  Vitreous  to  pearly  luster. 

BaS04.  May  contain  varying  amounts  of  the  oxides  of  strontium 
and  calcium;  also  silica,  clay,  or  organic  matter.  Colors  the  flame 
green. 


DESCRIPTIVE  MINERALOGY 


257 


Barite  is  a  common  and  widely  distributed  mineral.  It  occurs  in 
metalliferous  veins  associated  with  galena,  sphalerite,  fluorite,  chal- 
copyrite,  and  the  various  manganese  and  iron  minerals.  This  type  of 
occurrence  furnishes  most  of  the  finest  crystals  of  barite.  Thus,  Cornwall, 
Cumberland,  and  Derbyshire,  England;  Kapnik,  Transylvania;  Herren- 


FIG.  538.— Barite  (light)  with 
stibnite.      Transylvania. 


FIG.  539. — Barite.      Schemnitz, 
Hungary. 


grund,  Hungary;  Bohemia;  Marquette  County,  Michigan;  DeKalb, 
New  York;  Fort  Wallace,  New  Mexico.  Also  in  pockets  and  lenticular 
deposits  in  limestones,  and  associated  with  calcite  and  celestite.  De- 
posits of  this  character  are  mined  in  Georgia,  Missouri,  Tennessee,  Ken- 
tucky, Virginia,  and  North  and  South  Carolina. 


FIG.  540. — Barite  (crested).     Marquette  County,  Michigan. 

Barite  is  used  in  large  quantities  in  the  manufacture  of  "  ready  mixed  " 
paint,  lithopone,  wall  paper,  glass,  artificial  ivory,  and  insecticides. 
It  is  the  principal  source  of  the  various  barium  compounds.  Some 
varieties  are  used  for  ornamental  purposes. 

ANGLESITE,  PbSO4. 

Orthorhombic,  bipyramidal  class.  Crystals  are  frequently  highly 
modified,  and  may  be  prismatic  (Fig.  541),  tabular,  or  pyramidal  in  habit. 
Massive  varieties  are  compact,  granular,  or  nodular. 

17 


258 


MINERALOGY 


Distinct  basal  and  prismatic  cleavages.  Conchoidal  fracture.  Hard- 
ness 3.  Specific  gravity  6.1  to  6.4.  Colorless,  white,  yellow,  brown, 
green,  or  blue.  Adamantine  to  greasy  luster.  Transparent  to  opaque. 

PbSO4.  Usually  quite  pure.  Fuses  easily  in  a  candle  flame.  Occurs 
as  a  pseudomorph  after  galena.  Alters  to  cerussite. 


FIG.    541. — Angles! te    (prismatic)    in 
galena.     Tintic  District,  Utah. 


FIG.    542. — Crocoite.      Near 
Dundas,  Tasmania. 


Anglesite  is  a  common  oxidation  product  of  lead  minerals,  especially 
galena.  It  is  commonly  found  in  cracks  and  cavities  with  galena  and 
cerussite.  Other  associates  are  sphalerite,  smithsonite,  hemimorphite, 
and  limonite.  Excellent  crystals  are  found  at  Monte  Poni,  Sardinia; 
Clausthal,  Germany;  Anglesea,  England;  Leadhills,  Scotland;  Phoenix- 
ville,  Pennsylvania;  Tintic  district,  Utah;  various  places  in  Colorado, 
Missouri,  Wisconsin,  Arizona,  and  California;  in  large  deposits  in  Mexico 
and  Australia. 

Anglesite  is  an  ore  of  lead. 

Crocoite,  PbCrO4. 

Monoclinic,  prismatic  class.  Commonly  in  prismatic  or  acicular 
crystals,  often  highly  modified  and  striated  (Fig.  542).  Also  columnar, 
granular,  or  in  crusts. 

Distinct  basal  and  prismatic  cleavages.  Conchoidal  to  uneven  frac- 
ture. Hardness  2.5  to  3.  Specific  gravity  5.9.  to  6.1.  Various  shades 
of  red,  resembling  potassium  bichromate  in  color,  Orange  yellow  streak. 
Adamantine  luster  to  greasy.  Translucent. 

PbCr04.     Usually  quite  pure. 

An  alteration  product  of  galena  and  is  usually  associated  with  galena, 
quartz,  pyrite,  vanadinite,  wulfenite,  and  limonite.  Found  in  excellent 
crystals  near  Dundas,  Tasmania;  Siberia;  Maricopa  County,  Arizona. 

Not  a  common  mineral  and  of  no  commercial  importance. 


DESCRIPTIVE  MINERALOGY 


259 


Wolframite  Group 

The  members  of  this  group  crystallize  in  the  tetragonal  and  mono- 
clinic  series,  see  page  254.  The  various  tungstates  are  at  present  of 
great  commercial  importance. 

Wulfenite,  PbMoO4. 

Tetragonal,  tetragonal  pyramidal  class.  Usually  in  square  and  thin 
tabular  crystals  (Fig.  543).  Also  pyramidal  or  short  columnar.  Some- 
times with  third  order  forms.  Hemimorphic  development  very  rare. 
Also  in  coarse  to  fine  granular  masses. 

Hardness  3.  Specific  gravity  6.3  to  7. 
Resinous  to  adamantine  luster.  Various  shades 
of  yellow,  red,  or  green;  also  gray  or  white. 
Yellowish  white  streak.  Transparent  to  trans- 
lucent. 

PbMo04.  May  contain  some  calcium, 
vanadium,  molybdenum,  or  chromium.  Occurs 
as  a  pseudomorph  after  galena. 

Wulfenite  is  a  secondary  mineral,  usually  the 
result  of  the  decomposition  of  lead  minerals. 
It  is  commonly  associated  with  galena,  pyro- 
morphite,  and  vanadinite.  Occurs  in  Hungary; 
Saxony;  Phoenixville,  Pennsylvania;  various 
places  in  Yuma,  Maricopa,  and  Pinal  Counties,  Fl£-  543.— Wulfenite. 

A    -  i.  •    i.^    XT         j         i       •     o       xu  Bleiberg,  Austria. 

Arizona;  Searchlight,  Nevada;  also  in  Southamp- 
ton, Massachusetts;  Wisconsin,  New  Mexico,  and  California. 
A  source  of  molybdenum  and  its  compounds.     See  page  205. 


FIG.    544! 


FIG.  545. — Scheelite  on  quartz. 
Zinnwald,   Bohemia. 


Scheelite,   CaWO4. 

Tetragonal   tetragonal   bipyramidal   class.      Crystals  are   generally 
small  and  pyramidal  in  habit  (Figs.  544  and  545);  rarely  tabular;  some- 


260 


MINERALOGY 


times  with  third  order  forms.  More  often  as  crystalline  crusts  on  quartz, 
or  in  reniform,  disseminated,  or  granular  masses. 

Distinct  pyramidal  cleavage.  Conchoidal  to  uneven  fracture. 
Hardness  4.5  to  5.  Specific  gravity  5.9  to  6.2.  White,  yellow,  brown, 
green,  or  reddish.  Adamantine  to  greasy  luster.  Transparent  to 
opaque. 

CaWO4.  Usually  contains  some  molybednum.  Occurs  as  a  pseudo- 
morph  after  wolframite. 

Usually  found  with  quartz,  cassiterite,  fluorite,  topaz,  molybdenite, 
wolframite,  and  apatite.  Occurs  in  Cornwall  and  Cumberland,  England; 
Schaggenwald  and  Zinnwald,  Bohemia;  New  South  Wales;  New  Zealand; 
Tasmania;  Monroe  and  Trumbull,  Connecticut;  San  Bernardino  and  Kern 
counties,  California;  Cochise,  Final,  and  Santa  Cruz  counties,  Arizona; 
Jardine,  Montana;  White  Pine  and  Humboldt  counties,  Nevada. 

An  important  source  of  tungsten  and  its  compounds. 

Huebnerite,  MnWO4. 

Monoclinic,  prismatic  class.  Generally  in  long  fibrous,  bladed, 
(Fig.  546),  or  stalky  crystals  without  good  terminations.  Also  in  com- 
pact, lamellar,or  cleavable  masses. 

Clinopin  coidal  cleavage.  Hardness  4.5  to  5.5.  Specific  gravity  6.7 
to  7.3.  Brownish,  red,  brownish  black,  pale  yellow,  or  nearly  black  in 
color,  in  transmitted  light,  pale  ruby  red  to  yellow.  Submetallic  to 
resinous  luster.  Translucent  to  opaque.  Streak-yellow  to  yellow-brown. 


FIG.    546. — Huebernite    in 
quartz.     Pima  County,  Arizona. 


FIG.   54' 


FIG.  5  4  8  . —Wolframite. 
Trumbull,  Connecticut. 


Huebnerite,  MnWO4.  Usually  contains  iron  and  passes  over  into 
wolframite,  see  page  261. 

Occurs  in  quartz  veins  with  wolframite,  fluorite,  pyrite,  scheelite, 
galena,  tetrahedrite,  and  muscovite.  Thus,  in  Lemhi  County,  Idaho; 
White  Pine  County,  Nevada;  Ouray,  and  San  Juan  counties,  Colorado. 

An  important  source  of  tungsten  and  its  compounds. 


DESCRIPTIVE  MINERALOGY 


261 


WOLFRAMITE,  (Fe,Mn)WO4. 

Monoclinic,  prismatic  class.  Crystals  are  thick  tabular  or  short 
columnar,  and  often  quite  large  (Figs.  547  and  548).  Commonly  in 
bladed,  curved  lamellar,  or  granular  masses. 

Perfect  clinopinacoidal  cleavage.  Uneven  fracture.  Hardness  5 
to  5.5.  Specific  gravity  7.1  to  7.5.  Dark  gray,  reddish  brown,  brownish 
black,  or  iron  black  in  color.  Streak  varies  from  dark  red  brown  for 
manganiferous  varieties  to  black  for  those  containing  much  iron.  Greasy 
submetallic  luster.  Opaque.  Sometimes  slightly  magnetic. 

(Fe,Mn)W04.  An  isomorphous  mixture  of  MnWO4  and  FeW04  in 
which  the  composition  of  one  of  these  constituents  is  not  less  than  20  per 
cent,  and  the  other  not  over  80  per  cent.  Wolframite  is  therefore  inter- 
mediate between  huebnerite  and  ferberite.  Occurs  as  a  pseudomorph 
after  scheelite. 

Occurs  with  quartz,  mica,  fluorite,  cassiterite,  apatite,  scheelite, 
molybdenite,  huebnerite,  ferberite,  galena,  and  sphalerite.  Some  loca- 
lities are:  Cornwall,  England;  various  places  in  Saxony;  Zinnwald,  Bo- 
hemia; Siberia;  New  South  Wales;  Burma;  Malay  States;  Portugal; 
Black  Hills,  South  Dakota;  Monroe  and  Trumbull,  Connecticut.  Boulder 
County,  Colorado,  is  the  chief  producing  locality  in  the  United  States. 

Wolframite  is  a  source  of  tungsten  and  its  compounds.  Tungsten 
is  used  in  the  manufacture  of  "high  speed"  tool  steels  and  as  the  filament 
in  electric  incandescent  lamps;  sodium  tungstate  as  a  mordant  and  to 
render  cloth  inflammable;  tungstic  oxide  to  color  glass;  and  calcium 
tungstate  in  X-ray  apparatus. 


FIG.  549. — Ferberite.     Boulder  County,  Colorado. 

Ferberite,  FeWO4. 

Monoclinic,  prismatic  class.  Crystals  are  usually  tabular  and  in 
crested  aggregates.  Also  in  compact  and  granular  masses  (Fig.  549). 

Perfect  clinopinacoidal  cleavage.  Uneven  fracture.  Hardness  5. 
Specific  gravity  7.5.  Brown  to  black  in  color  and  streak.  Opaque. 

FeWO4.  Usually  contains  manganese  and  passes  over  into  wolfra- 
mite, see  above. 

Occurs  with  quartz,  hematite,  limonite,  molybdenite,  pyrite,  scheelite 


262  MINERALOGY 

wolframite,  and  sylvanite.     The  principal  occurrences  are  in  Boulder 
County,  Colorado. 

Uses  are  the  same  as  for  wolframite. 


Uraninite,  (Pitchblende],  UO3,  UO2,  PbO,  etc. 

Cubic,  hexoctahedral  class.  Crystals  generally  show  the  octahedron 
and  rhombic  dodecahedron,  but  are  rare.  Commonly  in  compact, 
botryoidal,  reniform,  curved  lamellar,  or  granular  masses.  Often  ap- 
parenty  amorphous  (Fig.  550). 

Conchoidal  to  uneven  fracture.  Hardness  3  to  6.  Specific  gravity 
4.8  to  9.7,  crystals  9  to  9.7.  Pitchy  to  submetallic  luster  on  fresh  frac- 
ture surfaces,  otherwise  dull.  Brown  to  black  in  color.  Dark  green, 
brown,  or  black  streak.  Non-magnetic. 

Composition  is  uncertain.  Is  considered  an  uranate  of  uranyl  and 
lead  with  varying  percentages  of  the  rare  earths  thorium,  cerium,  yttrium 
lanthanum,  and  erbium,  and  the  gases  nitrogen, 
argon,  and  helium.  May  also  contain  radium  and 
be  strongly  radio-active.  This  element  was  dis- 
covered in  uraninite  from  Joachimsthal,  Bohemia. 
Cleveite  is  a  variety  from  near  Arendal,  Norway, 
and  contains  thorium,  argon,  and  helium.  Nivenite 
is  characterized  by  about  10  per  cent,  of  the  earths 
of  the  yttrium  groups.  It  occurs  in  Llano  County, 
Texas.  Broggerite  occurs  on  the  Island  of  Moss, 
near  Christiania,  Sweden,  and  contains  consider- 
able thorium. 

FIG.  550.— Uraninite          As  a   primary  constituent  of  pegmatites  and 

hLsPthatbBohemia  J°aC"    granites>  associated  with  orthite,  thorite,  and  fer- 

gusonite,  it  is  found  in   the   Arendal  and   Moss 

districts,  Norway;  Sweden;  Branch ville,  Connecticut;  Mitchell  County, 
North  Carolina;  Llano  County,  Texas;  Black  Hills,  South  Dakota. 
With  lead,  silver,  bismuth,  and  tin  minerals  it  occurs  at  Joachimsthal 
and  Pribram,  Bohemia;  Johanngeorgenstadt,  Saxony;  Cornwall,  England; 
Gilpin  County,  Colorado. 

Uraninite  is  an  important  source  of  uranium  and  radium  compounds. 
Uranium  is  used  in  the  manufacture  of  special  grades  of  steels;  its 
compounds  for  coloring  glass  and  as  pigments  for  porcelain  painting.  As 
is  well  known,  radium  compounds  possess  important  chemical,  physical, 
and  medicinal  properties. 

ALUNITE  (Alum  Stone),  K2(A1.2OH)6(SO4)4. 

Hexagonal,  ditrigonal  scalenohedral  class.  Crystals  are  generally 
small  rhombohedrons  resembling  cubes,  often  with  curved  surfaces; 
more  rarely  tabular.  Commonly  compact,  granular,  fibrous,  or  earthy 
(Fig.  551). 


DESCRIPTIVE  MINERALOGY 


263 


Perfect  basal  cleavage.  Conchoidal,  splintery,  or  earthy  fracture. 
Hardness  3.5  to  4,  sometimes  harder  due  to  admixtures  of  quartz  and 
feldspar.  Tough.  Specific  gravity  2.58  to  2.8.  Colorless,  white,  yel- 
lowish, or  reddish.  Pearly  luster  on  cleavage  surfaces,  otherwise  vitreous. 
Transparent  to  translucent. 

K2(A1.2OH)6(SO4)4  May  contain  some  sodium.  Insoluble  in 
hydrochloric  acid  and  water. 

Alunite  occurs  in  irregular  deposits  and  in  veins  in  altered  feldspathic 
rocks,  such  as  rhyolites,  trachytes,  and  andesites.  Common  associates 
are  kaolin,  pyrite,  opal,  and  quartz.  Occurs  in  Hungary,  Greece,  France, 
Mexico,  and  Japan.  In  the  United  States  it  is  found  at  Silverton  and 
Cripple  Creek,  Colorado;  Mariposa  County,  California;  Morenci,  Ari- 
zona; in  large  quantities  with  gold  in.  the  Goldfield  district,  Nevada,  and 
Marysvale,  Utah.  


FIG.  551.— Alunite. 
Talfa,  Italy. 


FIG.  552. — Brochantite. 
quicamata,  Chile. 


Chu- 


Alunite  is  a  source  of  alum  and  potassium  sulphate,  which  is  ob- 
tained by  roasting  and  subsequent  leaching.  Some  of  the  Hungarian 
varieties  are  so  hard  and  tough  as  to  be  used  for  millstones. 

Bronchantite,  CuSO4.3Cu(OH)2. 

Orthorhombic,  bipyramidal  class.  Short  prismatic  and  acicular 
crystals  with  vertical  striations.  Also  reniform  with  fibrous  structure, 
and  as  drusy  crusts  (Fig.  552). 

Perfect  brachypinacoidal  cleavage.  Hardness  3.5  to  4.  Specific 
gravity  3.8  to  3.9.  Emerald  to  blackish  green  in  color.  Light  green 
streak.  Transparent  to  translucent.  Vitreous  to  pearly  luster. 

CuSO4.3Cu(OH)2.    Loses  water  at  300°C. 

A  secondary  copper  mineral,  commonly  associated  with  malachite, 
azurite,  cuprite,  chalcopyrite,  and  limonite.  Occurs  in  Hungary;  Ural 
Mountains;  Bolivia;  Chile;  Sonora,  Mexico;  in  various  copper  districts; 
Arizona;  Chaffee  County,  Colorado;  Tin  tic  district,  Utah. 

Of  minor  importance  as  a  copper  mineral. 


264 


MINERALOGY 


GYPSUM,  Selenite,  Satin  Spar,  Alabaster,  CaSO4.2H2O. 

Monoclinic,  prismatic  class.     Crystals  are  usually  simple  and  either 
tabular  or  prismatic  in  habit.     Sometimes  twinned  parallel  to  the  ortho- 


FIG.  553. — Gypsum  crystals — tabular,  contact  and 
penetration  twins. 


FIG.  556. — Gypsum  (columnar  or  "pencil 
rock").     Grand  Rapids,  Michigan. 


FIG.  557. — Gypsum : 
Variety,  satin  spar. 
Montmartre,  Paris, 
France. 


pinacoid,  yielding  contact  (swallow-tail)  and  penetration  twins  (Figs. 
553,  554  and  555).  Very  common  in  cleavable,  columnar  (Fig.  556), 
granular,  fibrous,  foliated,  or  earthy  masses. 

There  are  three  cleavages  parallel  to  (1)  clino- 
pinacoid,  (2)  positive  unit  hemi-pyramid,  and  (3) 
ortho pinacoid,  yielding  very  thin  and  smooth  folia, 
and  fibrous  and  conchoidal  surfaces,  respectively. 
Hardness  2.  Specific  gravity  2.2  to  2.4.  Vitreous 
to  pearly  or  silky  luster.  Colorless,  white,  gray, 
yellow,  brown,  reddish,  or  black.  Transparent 
to  opaque. 

CaSO4.2H2O.     Often  mixed  with  clay,  sand, 
or  organic  matter.     Yields  water  when  heated  and 
becomes  white  and  opaque.     Soluble  in  380  to 
460  parts  of  water. 
There  are  five  varieties  of  gypsum. 

(1)  Selenite. — This  includes   crystals  and   cleavable  masses,   and  is 
usually  colorless  and  transparent. 


FIG.  558. — Gypsum 
(polished)  .  Grand 
Rapids,  Michigan. 


DESCRIPTIVE  MINERALOGY  '  265 

(2)  Satin  Spar. — A  fibrous  variety  often  with  a  pronounced  silky 
luster  (Fig.  557).     Sometimes  used  in  cheap  jewelry. 

(3)  Alabaster. — A  massive   usually  fine   grained  variety  (Fig.  558). 
Sometimes  used  for  statuary  purposes.     . 

(4)  Rock  Gypsum. — A  compact  scaly  or  granular  variety,  often  very 
impure.     It  is  frequently  ground  and  used  as  a  fertilizer  under  the  name 
of  landplaster. 

(5)  Gypsite. — An  impure,  earthy  or  sandy  variety  occurring  abun- 
dantly in  Kansas,  Arizona,  New  Mexico,  and  Oklahoma. 

Gypsum  is  a  common  mineral  and  often  occurs  in  extensive  deposits 
of  great  thickness.  It  is  usually  found  with  limestones  and  shales,  and 
in  connection  with  salt  deposits.  Deposits  of  this  character  are  fre- 
quently of  great  commercial  importance.  Some  of  the  best  known  and 
most  extensively  worked  occurrences  are  in  central  and  western  New  York; 
Alabaster  and  Grand  Rapids,  Michigan;  Fort  Dodge,  Iowa;  Blue  Rapids, 
Gypsum  City,  and  Medicine  Lodge,  Kansas;  also  various  places  in 
Oklahoma,  Texas,  Oregon,  South  Dakota,  and  Wyoming.  Large  deposits 
occur  also  at  Hillsboro,  Albert  County,  New  Brunswick;  and  in  Nova 
Scotia.  Excellent  transparent  crystals  are  found  at  Ellsworth  and 
Canfield  in  Trumbull  County,  and  also  in  Mahoning  County,  Ohio;  very 
large  crystals  in  Wayne  County,  Utah.  New  York,  Michigan,  and  Iowa 
are  the  chief  producers  of  gypsum. 

Although  most  gypsum  is  the  result  of  deposition  from  solution,  it  is 
sometimes  formed  by  the  hydration  of  anhydrite,  in  volcanic  regions,  by 
the  action  of  sulphurous  vapors  upon  limestone,  and  in  metalliferous 
veins  by  the  action  of  sulphuric  acid  resulting  from  the  oxidation  of 
metallic  sulphides.  The  common  associates  are  halite,  celestite,  sulphur, 
aragonite,  dolomite,  calcite,  pyrite,  and  quartz. 

Ground  rock  gypsum  is  used  as  a  fertilizer  and  is  called  land  plaster. 
It  is  also  used  as  a  disinfectant,  flux  in  glass  and  porcelain  manufacture, 
retarder  in  cement,  and  to  weight  fertilizers.  Alabaster  is  used  for  sta- 
tuary and  decorative  purposes.  Satin  spar  and  a  small  amount  of 
selenite  are  used  in  cheap  jewelry  and  microscopy,  respectively.  It  is 
also  used  as  an  adulterant  of  foods,  medicines,  and  paints.  When  gyp- 
sum is  calcined  so  as  to  drive  off  1J^  molecules  of  water,  it  forms  plaster 
of  Paris,  which  has  the  property  of  setting  or  becoming  hard  after  being 
mixed  with  water.  Plaster  of  paris  is  used  in  very  large  quantities  in 
patent  wall  plasters,  stucco,  white  wash,  dentistry,  crayons,  casts,  and 
in  many  other  ways. 

Epsomite  (Epsom  Salt),  MgSO4.7H2O. 

Orthorhombic,  bisphenoidal  class.  Occasionally  in  nearly  square 
prismatic  crystals  (Fig.  559) .  Commonly  as  granular,  fibrous,  or  earthy 
masses,  or  in  crusts. 

Perfect    brachypinacoidal    cleavage.     Hardness    2    to    2.5.     Specific 


266  MINERALOGY 

gravity   1.7  to   1.8.     Colorless  or  white.     Transparent  to  translucent. 

Bitter  salty  taste. 

MgSO4.7H2O.     Soluble  in  water.     Non-hygroscopic. 

Epsomite  is  a  common  constituent  of  ocean,  salt  lake,  and  spring 

waters.  Thus,  it  occurs  in  the  springs  at  Epsom,  England;  Seidlitz 
and  elsewhere,  Bohemia;  Of  en,  Hungary.  As  an  altera- 
tion product  of  kieserite,  it  is  found  in  the  salt  deposits 
of*  Stassfurt,  Germany.  It  may  be  the  result  of  the 
action  of  sulphuric  acid  from  decomposing  sulphides  on 
serpentine,  talc,  magnesite,  or  other  magnesium  rocks. 
At  Montmartre,  near  Paris,  it  occurs  with  gypsum.  It 
is  also  found  in  limestone  caves  in  Kentucky,  Tennessee, 
and  Indiana,  and  in  crusts  on  the  alkali  plains  of  Utah, 
Nevada,  and  California.  With  mirabilite  it  occurs  in 

FIG.   559.  ' 

Albany  County,  Wyoming. 

Epsomite  is  used  in  medicine,  as  a  fertilizer  in  place  of  gypsum,  and 
as  a  coating  for  cotton  cloth. 

Melanterite  (Copperas),  FeSO4.7H2O. 

Monoclinic,  prismatic  class.  Crystals  are  very  rare.  Usually  as 
earthy,  fibrous  or  capillary  crusts  or  efflorescences. 

Conchoidal  to  earthy  fracture.  Hardness  2.  Specific  gravity  1.8  to 
1.9.  Various  shades  of  green  in  color,  often  yellowish  after  exposure. 
Vitreous  to  dull  luster.  Transparent  to  translucent.  Sweet,  astringent 
taste,  somewhat  metallic. 

FeSO4.7H2O.  Sometimes  contains  manganese,  magnesium,  copper, 
or  zinc.  Easily  soluble  in  water.  Loses  water  on  exposure  and  crumbles 
to  powder. 

Decomposition  product  of  iron  sulphide  minerals,  especially  pyrite, 
marcasite,  chalcopyrite,  and  pyrrhotite.  Some  localities  are:  Hartz 
Mountains;  Bodenmais,  Bavaria;  Falun,  Sweden;  Rio  Tin  to,  Spain. 
In  the  United  States,  it  is  generally  found  as  an  efflorescence  with  the 
sulphides  of  iron. 

Melanterite  does  not  occur  abundantly  enough  in  nature  to  be  of 
commercial  importance.  The  artificial  compound  is  used  in  large 
quantities  as  a  mordant  in  dyeing,  as  a  disinfectant,  and  in  the  manu- 
facture of  inks,  blueing,  and  pigments. 

Chalcanthite  (Blue  Vitriol,  Blue  Stone),  CuSO4.5H2O. 

Triclinic,  pinacoidal  class.  Rarely  as  small,  flat  crystals.  Generally 
in  crusts  with  reniform,  stalactitic,  or  fibrous  structure. 

Crystals  possess  imperfect  basal  and  prismatic  cleavages.  Con- 
choidal fracture.  Hardness  2.5.  Specific  gravity  2.1  to  2.3.  Vitreous 
to  dull  luster.  Deep  blue,  sky  blue,  or  greenish  blue  in  color.  White  to 
light  blue  streak.  Translucent.  Disagreeable  metallic  taste. 


DESCRIPTIVE  MINERALOGY  267 

CuS04.5H2O.  May  contain  iron.  Readily  soluble  in  water  yielding 
a  blue  solution,  especially  when  ammoniacal. 

Chalcanthite  is  an  alteration  product  of  copper  minerals,  such  as 
chalcopyrite,  chalcocite,  and  bornite.  Occurs  in  the  mines  of  the  Hartz 
Mountains;  also  in  Hungary;  Falun,  Sweden;  Rio  Tin  to,  Spain;  Chessy, 
France;  and  Cornwall,  England;  Wicklow,  Ireland.  It  was  formerly 
found  in  considerable  quantities  in  the  Bluestone  mine,  near  Reno, 
Nevada,  and  at  Copiapo,  Chile.  Found  also  in  the  waters  of  the  copper 
mines  of  Arizona  and  Montana.  The  copper  in  such  mine  water  is  re- 
covered by  precipitation  with  scrap  iron. 

Only  rarely  does  it  occur  in  sufficient  quantities  to  be  of  commercial 
importance.  The  artificial  compound  is  used  in  copper-plating,  in  bat- 
teries, as  a  mordant  and  preservative  of  timber,  and  for  spraying  plants. 

7.  ALUMINATES,  FERRITES,  AND  BORAXES 

Of  the  six  minerals  described  in  this  division,  five  have  analogous 
chemical  compositions  and  are  considered  as  forming  an  isodimorphous 
series. 

SPINEL  GROUP 

SPINEL  Mg(AlO2)2  Cubic 

MAGNETITE  Fe(FeO2)2  Cubic 

FRANKLINITE  (Fe,Mn,Zn)(FeO2)2  Cubic 

CHROMITE  (Fe,Cr)[(Cr,Fe)02]2  Cubic 

Chrysoberyl  Be(AlO2)2  Orthorhombic 


Colemanite  Ca2B6Ou.6H2O  Monoclinic 

Colemanite  is  the  only  borate  occurring  in  nature  in  sufficient  quan- 
tities to  be  of  any  commercial  importance. 

Spinel  Group 

Several  members  of  this  group  rank  among  the  very  important  min- 
erals. All  these  minerals  are  hard,  5.5  to  8.5;  those  with  metallic  luster 
are  the  softer,  varying  from  5.5  to  6.5. 

SPINEL,  Mg(AlO2)2. 

Cubic,  hexoctahedral  class.  Octahedral  crystals  (Fig.  560),  fre- 
quently in  combination  with  the  rhombic  dodecahedron  (Fig.  561) 
Contact  twins  are  common,  twinned  parallel  to  a  face  of  the  octahedron 
(Spinel  law) .  Generally  in  disseminated  or  loose  crystals,  or  in  rounded 
grains. 

Imperfect  octahedral  cleavage.  Hardness  7.5  to  8.  Specific  gravity 
3.5  to  4.5.  Vitreous  to  nearly  dull  in  luster.  All  colors,  but  chiefly  red, 
blue,  green,  brown,  and  black.  Transparent  to  opaque. 

Mg(AlO2)2.  Magnesium  maybe  replaced  by  iron,  zinc,  or  manganese; 
the  aluminum  by  ferric  iron  and  chromium.  Infusible. 

There  are  several  important  varieties: 


268 


MINERALOGY 


1.  Ruby  Spinel. — Deep  red  in  color,  transparent. 

2.  Rubicelle. — Yellow  or  orange  red  in  color. 

3.  Blue  Spinel. — Light  blue  in  color. 

4.  Pleonaste. — An  iron-magnesium  spinel.     Dark  green,   brown,   or 
black.     Usually  opaque  or  nearly  so. 

5.  Picotite. — Contains  chromium.     Black,  yellow,  or  greenish  brown. 
Translucent  to  nearly  opaque. 

6.  Gahnite. — Contains  considerable  zinc.     Commonly  in  fairly  large 
crystals.     Various  shades  of  green,  also  brown  or  black.     Translucent  to 
opaque. 


FIG.  560. — Spinel  (octahe- 
dron). Labelle  County,  Quebec, 
Canada. 


FIG.  561. — Spinel  (octahedron  and 
rhombic  dodecahedron)  in  calcite. 
Franklin  Furnace,  New  Jersey. 


Spinel  is  a  common  metamorphic  mineral  occurring  usually  in  granular 
limestones,  gneiss,  and  serpentine.  It  is  also  an  accessory  constituent 
of  basic  igenous  rocks.  Gem  spinels  are  frequently  found  in  placer 
deposits,  especially  in  Ceylon,  Burma,  and  Siam.  The  common  as- 
sociates are  calcite,  chondrodite,  corundum,  graphite,  and  olivine. 
Important  localities  are:  Aker,  Sweden;  Orange  and  St.  Lawrence  counties, 
New  York;  Franklin  Furnace,  New  Jersey;  Bolton,  Massachusetts; 
Macon  County,  North  Carolina. 

Transparent  red  and  blue  varieties  are  highly  prized  as  gems. 

MAGNETITE   (Magnetic  Iron  Ore,  Lodestone),  Fe(FeO2)2. 

Cubic,  hexoctahedral  class.  Octahedral  and  rhombic  dodecahedral 
crystals  are  very  common,  often  very  perfect  and  with  bright  surfaces. 
Striated  faces  are,  however,  not  infrequently  observed.  Twinned  ac- 
cording to  the  spinel  law,  yielding  contact  and  polysynthetic  twins. 
Crystals  are  sometimes  highly  modified  and  may  be  greatly  distorted 
(Fig.  562).  Usually  occurs  in  coarse  to  fine  grained  masses,  in  lamellar 
to  compact  aggregates,  as  disseminated  grains,  or  as  loose  grains  or 
sand;  more  rarely  dendritic,  especially  in  mica. 

Octahedral  parting.  Conchoidal  to  uneven  fracture.  Hardness  5.5 
to  6.5.  Specific  gravity  4.9  to  5.2.  Metallic,  submetallic,  to  dull 
luster.  Iron  black  color.  Black  streak.  Opaque.  Strongly  magnetic 
(Fig.  563). 

Fe(FeO2)2-     Commonly  written    Fe304.     May  contain  magnesium, 


DESCRIPTIVE  MINERALOGY 


269 


nickel,  manganese,  phosphorus,  or  titanium.  Fuses  with  difficulty. 
Alters  to  limonite  and  hematite  (martite).  Magnetite  occurs  as  a 
pseudomorph  after  pyrite,  hematite,  and  siderite. 

Magnetite  occurs  rather  widespread;  being  found  principally  as  (1) 
a  primary  constituent  of  basic  igneous  rocks,  such  diabase,  gabbro, 
nepheline  syenite,  and  basalt;  (2)  as  a  metamorphic  mineral;  and  (3) 


FIG.  562. — Magnetite  crystals — octahedron,  rhombic  dodecahedron,  tetragonal  trisocta- 

hedron,  striated. 

as  a  constituent  of  certain  river,  lake,  and  sea  sands,  called  black  sands. 
The  common  associates  are  chlorite  (Fig.  564),  hornblende,  pyroxene, 
feldspar,  quartz,  pyrite,  chalcopyrite,  epidote,  chromite,  garnet,  and 
ilmenite.  Large  deposits  are  found  in  Norway  and  Sweden ;  Ural  Moun- 
tains; Brazil;  Mineville,  New  York;  Cornwall,  Pennsylvania;  Oxford, 


FIG.  563. — Magnetite:  Va- 
riety, lodestone.  Magnet  Cove, 
Arkansas. 


FIG.  564  . — Magnetite 
(octahedron)  in  chloritic 
schist.  Zillerthal,  Tyrol. 


New  Jersey.  Black  sands  are  rather  widespread  in  Alaska,  California, 
Idaho,  Montana,  Colorado,  Oregon,  and  Washington.  They  sometimes 
carry  small  amounts  of  platinum.  Magnetite  from  Magnet  Cove, 
Arkansas,  is  usually  very  strongly  magnetic,  and  is  termed  lodestone. 

Magnetite  is  an  important  iron  ore.     About  5  per  cent,  of  all  the  iron 
ore  mined  annually  in  the  United  States  is  magnetite. 


270  MINERALOGY 

FRANKLINITE  (Fe,  Mn,  Zn)  (FeO2)2. 

Cubic,  hexoctahedral  class.  The  octahedron  is  rather  common,  some- 
times with  the  rhombic  dodecahedron  (Fig.  565)  and  with  rounded 
edges.  Occurs  usually  in  compact  and  granular  masses,  or  as  rounded 
grains. 

Imperfect  octahedral  cleavage.  Conchoidal  fracture.  Hardness 
5.5.  to  6.5.  Specific  gravity  5  to  5.2.  Metallic  or  dull  luster.  Iron 
black  in  color.  Brown,  reddish,  or  black  streak.  Often  slightly 
magnetic.  Opaque. 

(Fe,Mn,Zn)(FeO2)2-  The  composition  varies  greatly,  ZnO  from 
17  to  25  per  cent.,  MnO  10  to  12  per  cent.,  and  Fe2O3  about  60  per  cent. 

t    When  heated  becomes  strongly  magnetic. 

Infusible. 

Franklinite  occurs  extensively  in  the 
metamorphic  area  about  Franklin  Furnace 
and  Sterling  Hill,  Sussex  County,  New 
Jersey,  where  it  is  associated  with  willemite, 
zincite,  rhodonite,  and  calcite.  Also  found 

ln  Cubi°al 


FIG.  565. — Franklinite  (octa- 
hedron   and   rhombic   dodecahe-          Franklinite  is  a  source  of  zinc  which,  by 
dron)    with 'calcite.      Franklin    heating    the    mineral,   is   easily    obtained 

Furnace,  New  Jersey.  '  J 

either  as  spelter  or  zinc  oxide.     The  residue 

contains  about  12  per  cent,  of  manganese  and  40  per  cent,  iron,  and  is 
used  as  spiegeleisen  in  the  manufacture  of  steel. 

CHROMITE  (Chrome  Iron,  Chromic  Iron  Ore),  (Fe,Cr)  [(Cr,Fe)O2]2. 

Cubic,  hexoctahedral  class.  Rarely  in  octahedral  crystals.  Usually 
in  fine  granular,  compact  masses,  or  as  disseminated  grains. 

Indistinct  octahedral  cleavage.  Uneven  to  conchoidal  fracture. 
Hardness  5.5.  Specific  gravity  4.3  to  4.6.  Pitchy  submetallic  to  metallic 
luster.  Opaque.  Iron  black  to  brownish  black  in  color.  Dark  brown 
to  grayish  streak.  Sometimes  slightly  magnetic. 

(Fe,Cr)[(Cr,Fe)02]2.     May  contain  magnesium  and  aluminum. 

Chromite  occurs  usually  in  veins  and  irregular  masses  in  basic  magne- 
sium rocks,  especially  serpentine.  It  is  often  the  result  of  magmatic 
segregation.  The  common  associates  are  serpentine,  talc,  chrome 
garnet,  zaratite,  and  corundum.  It  occurs  at  Franckenstein,  Silesia; 
New  Zealand;  Rhodesia;  New  Caledonia;  Asiatic  Turkey;  Texas;  Lan- 
caster County,  and  elsewhere  in  Pennsylvania;  Baltimore  County, 
Maryland;  Shasta  and  other  counties  in  California;  also  in  North  Caro- 
lina, Oregon,  Washington,  and  Wyoming.  Also  found  in  platinum  placers 
and  in  black  sands. 

Chromite  is  used  in  the  manufacture  of  refractory  chrome  bricks 
and  furnace  linings;  for  making  special  grades  of  steels,  such  as  ferro- 


DESCRIPTIVE  MINERALOGY 


271 


chrome  used  for  cutting  tools,  projectiles,  and  armor  plate;  also  for  the 
production  of  pigments,  dyes,  and  mordants,  and  in  tanning. 

Chrysoberyl,  Be(AlO2)2. 

Orthorhombic,  bipyramidal  class.  Crystals  are  tabular,  also  heart- 
shaped  and  pseudohexagonal  twins;  frequently  striated  (Figs.  566,  567 
and  568).  Also  as  crystal  fragments,  and  loose  or  rounded  grains. 

Distinct  brachypinacoidal  cleavage.  Conchoidal  fracture.  Hard- 
ness 8.5.  Specific  gravity  3.5  to  3.8.  Vitreous  to  greasy  luster.  Green- 
ish white,  greenish  yellow,  and  asparagus  to  emerald  green  in  color; 
often  red  in  transmitted  light.  Transparent  to  translucent.  Some 
varieties  have  a  bluish  opalescence  or  chatoyancy. 


FIG.  566. 


FIG.  567. — Chrysoberyl  (twin). 
Haddam,  Connecticut. 


FIG.    568. 


Be(AlO2)2.  May  contain  some  iron  and  chromium.  Infusible. 
Insoluble  in  acids. 

There  are  three  varieties: 

(1)  Ordinary  Chrysoberyl.     Usually  green  or  pale  green  in  color. 

(2)  Alexandrite.     Emerald  green  in  color,  but  red  in  transmitted  gas  or 
lamp  light;  with  tungsten  light,  intermediate  between  red  and  green. 

(3)  Cat's  Eye  or  Cymophane.     An  opalescent,  yellow  green  variety. 

Chrysoberyl  is  usually  found  in  gneiss,  mica  schist,  or  granite.  Com- 
mon associates  are  beryl,  tourmaline,  garnet,  apatite,  and  sillimanite. 
It  occurs  in  the  Ural  Mountains;  Haddam,  Connecticut;  Norway  and 
Stoneham,  Maine;  Greenfield,  New  York;  as  rounded  pebbles  in  the  gem 
placers  of  Ceylon,  Tasmania,  and  Brazil. 

Transparent  varieties  are  highly  prized  as  gems. 


Colemanite,  Ca2B6Oii.5H2O. 

Monoclinic,  prismatic  class.  Crystals  are  usually  short  prismatic 
and  resemble  datolite  (Fig.  569) ;  often  highly  modified.  Also  in  compact, 
granular,  and  cleavable  masses,  which  resemble  chalk  or  porcelain. 

Highly  perfect  clinopinacoidal  cleavage.  Uneven  to  subconchoidal 
fracture.  Hardness  3.5  to  4.5.  Specific  gravity  2.4.  Vitreous  to  dull 
luster.  Colorless  to  white.  Transparent  to  opaque. 

Ca2B6On.5H2O.     Easily  soluble  in  hot  hydrochloric  acid.     Boracic 


272 


MINERALOGY 


acid  separates  on  cooling.     Insoluble  in  water.     Treated  with  sodium 
carbonate  or  sulphate  it  yields  borax,'  Na2B4O7.1OH20. 

Commonly  associated  with  halite,  thenardite, 
trona,  gypsum,  celestite,  and  quartz.  As  a  lake 
deposit  it  occurs  extensively  in  San  Bernardino, 
Inyo,  Los  Angeles,  and  Ventura  counties,  Cali- 
fornia. 

Colemanite  is  the  chief  source  of  borax,  which 
is  used  extensively  in  the  manufacture  of  soap, 
enamels,  glass,  washing  powders,  ointments,  and 
lotions;  also  in  welding,  soldering,  assaying,  and 
blowpiping,  as  an  antiseptic,  and  in  the  preserva- 
tion of  meat  and  fish. 


8.  PHOSPHATES,  COLUMBATES,  AND 

VANADATES 

FIG.    569. — Colemanite 

A  lar^e  number  of  minerals  belonging  to  this 
division  have  been  recorded  in  the  literature,  but 
only  seven  are  of  sufficient  importance  to  warrant  a  description. 


Monazite 
COLUMBITE 

APATITE 

PYROMORPHITE 

Vanadinite 

Wavellite 
Turquois 
Carnotite 


(Ce,La,Di)P04 

(Fe,Mn)[(Cb,Ta)03]2 
APATITE  GROUP 

Ca5F(P04)3 

Pb5Cl(P04)3 

Pb5Cl(V04)3 


(A1.OH)3(P04)2.5H2O 

H6[Al(OH)2]6Cu(OH)(P04)4 
K20.2U03.V205.3H2O 


Monoclinic 
Orthorhombic 

Hexagonal 
Hexagonal 
Hexagonal 

Orthorhombic 

Triclinic 

Orthorhombic 


Columbite  is  a  salt  of  metatantalic  acid,  H2Ta03.  The  phosphates 
can  be  referred  to  the  orthophosphoric  acid,  H3PO4,  while  vanadinite 
is  a  derivative  of  a  corresponding  acid,  H3VO4. 

Monazite,    (Ce,La,Di)PO4. 

Monoclinic,  prismatic  class.  Crystals  are  thick  tabular  or  square 
prismatic,  usually  small  and  not  common.  Generally  found  as  angular 
disseminated  masses  and  rolled  grains  in  sand. 

Perfect  basal  cleavage.  Conchoidal  fracture.  Hardness  5  to  5.5. 
Specific  gravity  4.9  to  5.3.  Brownish  gray,  yellow,  or  reddish  in  color. 
White  streak.  Resinous  luster.  Translucent  to  opaque. 

(Ce,La,Di)PO4.  May  contain  from  J£  to  20  per  cent,  of  ThO2. 
Commercial  monazite  sand  contains  usually  from -2. 5  to  5  per  cent. 
Th02. 

Occurs   disseminated   in   granites   and   gneisses,    thus,    at   Arendal, 


DESCRIPTIVE  MINERALOGY  273 

Xorway;  Miask,  Ural  Mountains;  Binnenthal,  Switzerland;  Amelia 
Court  House,  Virginia.  The  most  important  occurrence  of  monazite  is 
as  sand,  extensive  deposits  of  which  are  found  in  the  western  part  of 
North  and  South  Carolina  and  Georgia;  in  the  provinces  of  Bahia,  Minas 
Geraes,  Rio  de  Janeiro,  and  Sao  Paulo,  Brazil;  Travancore,  India;  also 
in  the  Ural  Mountains.  Common  associates  are  magnetite,  zircon, 
garnet,  ilmenite,  thorite,  gold,  chromite,  and  sometimes  the  diamond. 

Monazite  is  the  chief  source  of  thorium  dioxide  which  is  used  exten- 
sively in  the  manufacture  of  incandescent  mantles.  United  States 
consumes  about  one-fourth  of  the  thorium  nitrate  used  in  the  world. 
Most  of  the  world's  supply  is  obtained  from  Brazil. 

COLUMBITE,    (Fe,Mn)[(Cb,Ta)O3)]2. 

Orthorhombic,  bipyramidal  class.  Short  prismatic  or  thick  tabular 
crystals,  often  resembling  those  of  wolframite.  Also  massive  and 
disseminated. 

Brachypinacoidal  cleavage.  Conchoidal  to  uneven  fracture,  often 
with  iridescent  tarnish.  Hardness  6.  Specific  gravity  5.4  to  6.4. 
Brown  to  iron  black  in  color.  Brownish,  reddish,  or  black  streak. 
Greasy,  submetallic  to  dull  luster. 

(Fe,Mn)[(Cb,Ta)O3)]2.  Composition  varies  greatly.  Frequently 
containing  tin  and  tungsten.  When  tantalum  predominates  it  is  called 
tantalite.  Infusible.  Not  attacked  by  acids. 

Columbite  occurs  in  granite  pegmatites,  associated  with  beryl,  tour- 
maline, spodumene,  lepidolite,  cryolite,  quartz,  feldspar,  wolframite, 
and  cassiterite.  It  occurs  at  Ivigtut,  Western  Greenland;  Bodenmais, 
Bavaria;  Miask,  Ural  Mountains;  Western  Australia;  Standish,  Maine; 
Branchville,  Connecticut;  Mitchell  County,  South  Carolina;  Black 
Hills,  South  Dakota;  Amelia  County,  Virginia. 

An  important  source  of  columbium  and  tantalum.  Filaments  of 
tantalum  have  been  used  in  electric  incandescent  lamps. 

Apatite  Group 

This  group  contains  the  calcium  and  lead  salts  of  orthophosphoric 
and  orthovanadic  acids.  These  minerals  form  an  interesting  isomorphous 
series. 

APATITE,   Ca5F(PO4)3. 

Hexagonal,  hexagonal  bipyramidal  class.  Prismatic  and  thick  tabular 
crystals  are  common,  often  well  developed  and  highly  modified.  Some- 
times large.  The  edges  may  be  rounded  and  have  a  fused  appearance. 
At  times  forms  of  the  third  order  are  to  be  observed  (Fig.  570).  Also 
in  compact,  fibrous,  nodular,  reniform,  oolitic,  or  earthy  masses. 

Imperfect  basal  cleavage.     Conchoidal  fracture.     Hardness  5.     Spe- 


274  MINERALOGY 

cific  gravity  3.1  to  3.2.  Sometimes  colorless  and  transparent,  but  usually 
translucent  to  opaque  and  variously  colored,  brown,  green,  gray,  yellow, 
red,  or  white.  The  color  is  often  unevenly  distributed.  Vitreous  to 
greasy  luster. 

Apatite  is  essentially  an  orthophosphate  of  calcium  containing 
fluorine,  chlorine,  or  hydroxyl  in  varying  amounts.  Hence,  the  following 
formulas  have  been  assigned  to  it,  Ca5F(P04)3,  Ca5Cl(PO4)3  and  Ca5- 
(C1,F,OH)(PO4)3.  Fluorine  usually  predominates,  fluor-apatite  being 
more  common  than  Mow-apatite.  Magnesium,  manganese,  and  iron 
may  also  be  present.  Fuses  with  difficulty.  Easily  soluble  in  acids. 
May  phosphoresce  when  heated. 

There  are  three  important  varieties : — 

(1)  Ordinary  Apatite.  This  includes  crystallized,  cleavable,  and 
granular  varieties. 


FIG.  570. — Apatite  crystals — prismatic,  fused  edges  FIG.  571. — Apatite  in  calcite. 

and   corners,  tabular.  Franklin  Furnace,  New  Jersey. 

(2)  Phosphate  Rock. — An  impure  massive  variety  containing  15  to 
40  per  cent,  of  P2O5      Color  is  gray,  white,  brown,  or  black.     The  hard- 
ness varies  from  2  to  5.     It  occurs  in  beds,  or  as  nodules  and  concretions. 

(3)  Guano. — Animal  excrement,  chiefly  of  birds,  rich  in  phosphoric 
acid.     Gray  to  brown  in  color,  and  porous,  granular,  or  compact  in 
structure. 

Apatite  is  a  common  accessory  constituent  of  many  igneous  rocks. 
It  is  an  associate  of  metalliferous  ore  deposits,  especially  those  of  magne- 
tite and  cassiterite.  It  occurs  also  in  granular  limestones  (Fig.  571), 
and  in  fact  is  present  in  small  quantities  in  nearly  all  types  of  rocks. 
Common  associates  are  calcite,  cassiterite,  quartz,  fluorite,  wolframite, 
and  magnetite.  Some  important  localities  are:  Ehrenfriedersdorf, 
Saxony;  Schlaggenwald,  Bohemia;  St.  Gothard,  Switzerland;  Knappen- 
wand,  Tyrol;  Japan;  Renfrew  County,  Ontario ;  Ottawa  County,  Quebec; 
Norwich  and  Bolton,  Massachusetts;  St.  Lawrence  and  Jefferson 
counties,  New  York;  Chester  County,  Pennsylvania;  Franklin  Furnace, 
New  Jersey;  Auburn,  Maine. 


DESCRIPTIVE  MINERALOGY  275 

Phosphate  rock  occurs  in  extensive  deposits  in  Florida,  South  Caro- 
lina, Tennessee,  Pennsylvania,  Arkansas,  Wyoming,  Idaho,  Utah,  and 
Montana. 

Phosphate  rock  is  used  in  enormous  quantities  in  the  manufacture  of 
fertilizers,  its  phosphoric  acid  content  being  rendered  available  by  treat- 
ing with  sulphuric  acid.  Apatite  is  also  used  to  some  extent  as  a  source 
of  phosphorous. 

PYROMORPHITE,  Pb5Cl(PO4)3. 

Hexagonal,  hexagonal  bipyramidal  class.  Crystals  are  usually 
small,  rounded,  or  barrel-shaped  (Fig.  572).  Often  hollow  and  skeletal, 
or  in  parallel  groups.  Sometimes  they  resemble  those  of  apatite.  Occurs 
also  in  botryoidal  and  reniform  aggregates,  disseminated,  and  in  crusts. 

Conchoidal  to  uneven  fracture.  Hardness  3.5  to  4.  Specific  gravity 
6.9  to  7.1.  Usually  some  shade  of  green,  but  may  be  yellow,  gray,  brown, 
orange,  or  white.  White  to  pale  yellow  streak.  Greasy  to  adamantine 
luster.  Translucent  to  opaque. 

Pb5Cl(PO4)3.  May  contain  calcium,  fluorine,  or  arsenic.  Occurs  as 
a  pseudomorph  after  galena  and  cerussite. 

Pyromorphite  is  generally  a  secondary 
mineral  formed  from  the  decomposition 
of  lead  ores.  Common  associates  a.re 
galena,  cerussite,  barite,  and  limonite.  It 
occurs  in  the  Freiberg  district,  Saxony; 
Clausthal,  Hartz  Mountains;  Ems,  Nas- 
sau; Cornwall  and  Cumberland,  England; 
Phoenixville,  Pennsylvania;  Lubec  and 

T  -*  r    •          T        ii'noi        i        1^1  FIG.  572. — Pyromorphite.     Ems, 

Lenox,  Maine;  Lead  hill,  Scotland;  Coeur  Nassau,  Germany. 

d'Alene,  Idaho. 

A  minor  source  of  lead. 

Vanadinite,  Pb5Cl(VO4)3. 

Hexagonal,  hexagonal  bipyramidal  class.  Crystals  are  usually 
prismatic,  often  skeletal  and  resembling  those  of  pyromorphite.  Occurs 
also  compact,  fibrous,  globular,  and  in  crusts. 

Uneven  to  cpnchoidal  fracture.  Hardness  3.  Specific  gravity  6.7 
to  7.2.  Yellow,  brown,  or  red  in  color.  White  to  pale  yellow  streak. 
Translucent  to  opaque.  Resinous  luster. 

Pb5Cl(VO4)3.  May  contain  phosphorous  or  arsenic.  Endlichite  is 
a  light  yellow  variety  containing  arsenic.  Fuses  easily.  Readily  soluble 
in  nitric  acid. 

Occurs  associated  with  lead  minerals,  but  never  in  large  quantities. 
Some  localities  are:  Zimapan,  Mexico;  Ural  Mountains;  various  places 
in  Yuma,  Maricopa,  Final,  and  Yavapai  Counties,  Arizona;  Kelley, 
New  Mexico. 

It  is  a  source  of  vanadium  and  its  compounds. 


276 


MINERALOGY 


Wavellite  (ALOH)3(PO4)2. 5H2O. 

Orthorhombic,  bipyramidal  class.  Good  crystals  are  very  rare. 
Usually  in  crystalline  crusts,  or  hemispherical  or  globular  masses  made 
up  of  concentric  layers  and  possessing  a  radial  fibrous  structure  (Fig. 
573). 

Conchoidal  to  uneven  fracture.  Hardness  3.5  to  4.  Specific  gravity 
2.3  to  2.4.  May  be  colorless,  but  is  usually  gray,  yellow,  green,  blue,  or 
black.  Vitreous  luster.  Translucent. 

(A1.OH)3(PO4)2.5H2O.  —  The  water  of  crystallization  may  vary. 
Some  varieties  contain  fluorine.  Infusible.  Soluble  in  hydrochloric 
acid. 

Wavellite  is  a  secondary  mineral  formed  by  the  action  of  circulating 
waters  containing  phosphoric  acid  upon  rocks  and  minerals  rich  in  alumina. 
It  is,  hence,  found  on  the  surfaces  of  such  rocks,  or  lining  the  cracks  and 
cavities  in  the  same.  Some  localities  are:  Devonshire  and  Cornwall, 
England;  Bohemia;  Chester  and  York  Counties,  Pennsylvania;  Mont- 
gomery and  Garland  Counties,  Arkansas;  Silver  Hill,  South  Carolina. 


FIG.  573.— Wavellite.      Arkansas. 


FIG.  574. — Turquois.     Los 
Cerrillos,  Mexico. 


Turquois,  H6[A]  (OH) 2]6Cu(OH)  (PO4)4. 

Triclinic.  Crystals  are  tabular  but  very  rare.  Usually  apparently 
amorphous,  in  reniform,  botryoidal,  or  stalactitic  masses  and  in  veins; 
also  as  crusts,  coatings  (Fig.  574)  and  disseminated  grains,  or  rolled  and 
rounded  pebbles. 

Conchoidal  fracture.  Hardness  6.  Specific  gravity  2.6  to  2.8. 
Various  shades  of  blue  or  green.  Bluer  in  artificial  light.  Translucent 
to  opaque.  Waxy  to  dull  luster.  White  or  slightly  greenish  streak. 

H5[Al(OH)2]6Cu(OH)(P04)4.  Infusible.  Soluble  in  acids  after 
ignition. 

Turquois  is  a  secondary  mineral  and  is  often  associated  with  limonite, 
quartz,  feldspar,  or  kaolin.  It  occurs  in  trachyte  near  Nishapur  in 
the  province  of  Khorassan,  Persia;  Los  Cerillos  and  elsewhere,  New 
Mexico;  Turquois  Mountain,  Arizona;  San  Bernardino  County,  Cali- 
fornia; Nye  County,  Nevada;  Colorado. 

Used  as  a  gem  mineral.     Color  fades  in  time  and  is  destroyed  by  heat. 


DESCRIPTIVE  MINERALOGY  277 

Carnotite,  K2O.2UO3.V2O5.3H2O. 

Orthorhombic.  Crystals  are  small,  tabular,  and  with  a  rhombic 
outline.  Usually  observed  in  scaly  aggregates,  incrustations,  or  as  a 
crystalline  powder. 

Perfect  basal  cleavage.  Earthy  fracture.  Hardness  1  to  2.  Canary 
to  lemon  yellow  in  color.  Resinous  to  dull  luster.  Transparent  to 
translucent. 

A  vanadate  of  potassium  and  uranium,  containing  small  amounts  of 
radium. 

Occurs  as  a  powdery  incrustation  in  loosely  cohering  masses,  or  as  an 
impregnation  in  sand  or  sandstone.  Common  associates  are  malachite, 
azurite,  biotite,  and  magnetite.  Occurs  in  Montrose  County,  Colorado; 
San  Juan  County,  Utah;  Mauch  Chunk,  Pennsylvania;  Radium  Hill, 
South  Australia. 

An  important  source  of  radium. 

9.   SILICATES  AND  TITANATES 

This  division  contains  a  very  large  number  of  minerals,  some  of 
which  are  exceedingly  common.  For  example,  the  members  of  the 
groups,  known  as  the  feldspars,  pyroxenes,  amphiboles,  and  micas,  are 
very  abundant  and  important  as  rock  minerals.  The  feldspars  alone 
make  up  60  per  cent,  of  the  igneous  rocks.  For  the  most  part, 
the  chemical  composition  of  these  minerals  is  rather  complex.  In  fact, 
in  many  cases,  it  is  difficult  to  interpret  a  chemical  analysis  of  a  silicate 
mineral  correctly,  because  the  substance  may  be  considered  as  a  salt 
of  several  silicic  acids. 

Orthosilicic  acid,  H4SiO4,  is  taken  as  the  basis  for  the  derivation  of  the 
other  silicic  acids.  By  the  loss  of  a  molecule  of  water,  it  passes  over  to 
the  metasilicic  acid,  H2SiO3.  By  the  loss  of  water  from  several  mole- 
cules of  these  acids,  the  more  complex  acids  may  be  derived,  as  follows: 

Orthosilicic  acid  H4SiO4 

Diorthosilicic  acid  H6Si2O7  (2H4SiO4  -  H20) 

Trisilicic  acid  H4Si3O8  (3H4SiO4  -4H2O) 

Dimetasilicic  acid  H2Si2O5  (2H2SiO3  -  H20) 

The  polysilicic  acids  are  still  more  complex. 

The  following  minerals  include  the  most  abundant  and  important 
silicates : 

STAUROLITE  HFeAl5Si2Oi3  Orthorhombic 

HEMIMORPHITE       H2Zn2SiO5  Orthorhombic 

ANDALUSITE  GROUP 

ANDALUSITE  Al2SiO6  Orthorhombic 

Sillimanite  AlaSiOs  Orthorhombic 

CYANITE  Al2SiO5  Triclinic 


278 


MINERALOGY 


TOPAZ  Al2(F,OH)2SiO4  Orthorhombic 

Datolite                           Ca(B.OH)SiO4  Monoclinic 

TOURMALINE              H2oB2Si4O2i  Hexagonal 

Chondrodite                    [Mg(F,OH)]2Mg3(SiO4)2  Monoclinic 

EPIDOTE  GROUP 

EPIDOTE                       Ca2(Al,Fe)2(Al.OH)(SiO4)3  Monoclinic 

Orthite                             Ca2(Al,Ce,Fe)2(Al.OH)(SiO4)3  Monoclinic 

VESUVIANITE              Ca6[Al(OH,F)]Al2(SiO4)5  Tetragonal 

OLIVINE  GROUP 


OLIVINE 

(Mg,Fe)2Si04. 

Orthorhombic 

Willemite 

Zn2SiO4 

Hexagonal 

GARNET 

R"3R'"2(Si04)3 

Cubic 

CHRYSOCOLLA 

CuO,SiO2,H2O                     Hexagonal 

or  Tetragonal 

MICA  GROUP 

BIOTITE 

(K,H)2(Mg,Fe)2(Al,Fe)2(Si04)3 

Monoclinic 

PHLOGOPITE 

(K,H)3Mg3Al(SiO4)3 

Monoclinic 

MUSCOVITE 

H2KAl3(SiO4)3 

Monoclinic 

Lepidolite 

(Li,K)2(F,OH)2Al2Sis09 

Monoclinic 

CHLORITE 

H8Mg5Al2Si3018 

Monoclinic 

SERPENTINE 

H4Mg3Si2O9 

Monoclinic 

TALC 

H2Mg3Si4Oi2 

Monoclinic 

Sepiolite 

H4Mg2Si3Oi0 

Monoclinic 

Garni  erite 

H2(Ni,Mg)SiO4 

Amorphous 

KAOLINITE 

H4Al2Si2O9 

Monoclinic 

NEPHELITE 

(Na,K)8Al8Si9034 

Tetragonal 

Cancrinite 

H6(Na,,Ca)4(NaCO3)2Al8Si9O36 

Hexa-gonal 

Sodalite 

Na4Al2(AlCl)(Si04)3 

Cubic 

Lazurite 

(Na2,Ca)2Al2[Al(NaSO4,NaS3,Cl)](SiO 

4)3             Cubic 

Ilmenite 

FeTiOs 

Hexagonal 

PYROXENE  GROUP 

ENSTATITE 

(Mg,Fe)2(Si03)2 

Orthorhombic 

DIOPSIDE 

CaMg(SiO3)2 

Monoclinic 

Wollastonite 

Ca2(Si03)2 

Monoclinic 

AUGITE 

Pectolite 

SPODUMENE 

RHODONITE 


Tremolite 
Actinolite 

HORNBLENDE 

Leucite 
BERYL 


(Mg,Fe)Ca(Si03)(Si03) 
(Mg,Fe)Al(A103)(Si03)      [ 
(Mg,Fe)Fe(Fe03)(Si03)    J 
(Ca,Na2)2(Si03)2 
LiAl(SiO3)2 
Mn2(SiOs)2 

AMPHIBOLE  GROUP 

CaMg3(SiO3)4 

Ca(Mg,Fe)3(Si03)4 

Ca(Mg,Fe)3(SiO3)2(Si03)2 

Al2(Mg,Fe)3(AlO3)2(Si03)2 

Fe2(Mg,Fe)3(FeO3)2(SiO3)2 

K2Al2Si4012 

Be3Al2(SiO3)6 


Monoclinic 

Monoclinic 

Monoclinic 

Tri  clinic 


Monoclinic 
Monoclinic 

Monoclinic 

Pseudocubic 
Hexagonal 


DESCRIPTIVE  MINERALOGY 


279 


ORTHOCLASE 
MICROCLINE 
ALBITE 
LABRADORITE 

Anorthite 

SCAPOLITE 
TITANITE 


Natrolite 

ANALCITE 

APOPHYLLITE 

STILBITE 

CHABAZITE 


FELDSPAR  GROUP 

KAlSi3O8 
KAlSi3O8 
NaAlSi308(Ab) 
AbiAni  to  AbiAn3 
CaAl2Si2O8(An) 


(  nNa4A!3Si9024Cl    1 


CaTiSiOo 

ZEOLITES 

Na2Al(AlO)(Si03)3.2H2O 
Na2Al2(SiO3)4.2H2O 
Hi4K2Ca8(Si03)16.9H20 
(Ca,Na2)Al2Si60lc.6H20 
Ca  Al2Si6Oi6.8H20 


Monoclinic 
Triclinic 
Triclinic 
Triclinic 
Triclinic 

Tetragonal 
Monoclinic 


Monoclinic 
Cubic 
Tetragonal 
Monoclinic 
Hexagonal 


These  minerals  are  in  general  easily  distinguished  by  their  hardness, 
transparency,  non-metallic  luster,  lack  of  characterizing  colors,  and  un- 
colored  streak. 


STAUROLITE,  HFeAl5Si2Oi3. 

Orthorhombic,  bipyramidal  class.  Generally  in  well-developed 
prismatic  crystals,  consisting  of  the  unit  prism,  basal  and  brachypinacoids, 
and  a  macrodome.  Penetration  twins  ac- 
cording to  two  laws  are  common,  yielding 
cross-  or  plus-shaped  and  x-shaped  twins 
(Fig.  575). 

Brachypinacoidal  cleavage.  Conchoidal 
to  uneven  fracture.  Hardness  7  to  7.5. 
Specific  gravity  3.4  to  3.8.  Usually  reddish 
brown  in  color;  also  brownish  black,  yellow- 
ish brown,  or  gray  when  altered.  Colorless 
streak  when  fresh.  Vitreous  to  dull  luster. 
opaque,  rarely  transparent. 


••t 


FIG.  575. — Staurolite  crystals 
— simple,  plus-  and  X-shaped 
twins. 

Commonly  translucent  to 


FIG.  576. — Staurolite  in  schist. 
Falls,  Minnesota. 


Little 


FIG.  577. — Staurolite  (dark)   in  para- 
gonite  schist.     Tepin,  Switzerland. 


280 


MINERALOGY 


HFeAl5Si2Oi3.  Composition  varies  greatly.  May  contain  magne- 
sium, manganese,  and  zinc.  Often  quite  impure.  Infusible.  Insol- 
uble in  acids.  . . 

Occurs  generally  in  metamorphic  rocks,  especially  gneiss,  mica  schists, 
and  slates  (Fig.  576).  The  common  associates  are  cyanite,  garnet, 
tourmaline,  and  sillimanite.  In  the  Saint  Gothard  district,  Switzerland, 
it  occurs  with  cyanite  in  paragonite  (soda  mica)  schist  (Fig.  577); 
also  in  Tyrol;  France;  Brazil;  Fannin  and  Cherokee  Counties,  Georgia; 
Patrick  County,  Virginia;  Ducktown,  Tennessee;  Grantham,  New  Hamp- 
shire; Windham,  Maine;  Chesterfield,  Massachusetts;  Litchfield, 
Connecticut. 

Clear  and  transparent  crystals  are  sometimes  used  for  gem  purposes. 

HEMIMORPHITE  (Calamine),  H2Zn2SiO5. 

Orthorhombic,  pyramidal  class.  Crystals  are  usually  thin  tabular 
or  pyramidal  in  habit,  sometimes  showing  a  pronounced  hemimorphic 
development  (Fig.  579).  Often  arranged  in  sheaf -like  or  crested  groups 
(Fig.  579).  More  commonly  in  fibrous,  globular,  granular,  or  porous 
and  earthy  masses. 

Prismatic  cleavage.  Uneven  to  conchoidal  fracture.  Hardness  4.5 
to  5.  Specific  gravity  3.3  to  3.5.  Colorless,  white,  brown,  green,  or 
bluish.  Transparent  to  opaque.  Vitreous  to  dull  luster. 


FIG.  578. 


FIG.  579. — Hemimorphite.     Chihuahua, 
Mexico. 


H2Zn2SiO5.  Fuses  with  difficulty.  Gelatinizes  easily  with  acids. 
Occurs  as  a  pseudomorph  after  calcite,  galena,  dolomite,  fluorite,  and 
pyromorphite. 

Hemimorphite  is  a  secondary  mineral,  formed  by  the  action  of  silica 
bearing  water  upon  other  zinc  ores,  and  is  usually  found  in  limestones 
associated  with  smithsonite,  sphalerite,  galena,  cerussite,  and  anglesite. 
It  is  often  intimately  mixed  with  smithsonite.  Some  localities  are: 
Aachen,  Germany;  Raibel  and  Bleiberg,  Austria;  Silesia;  Cumberland 
and  Derbyshire,  England ;  Sardinia;  Sussex  County,  New  Jersey;  Phoenix- 
ville  and  Friedensville,  Pennsylvania;  Granby  and  elsewhere,  Missouri; 


DESCRIPTIVE  MINERALOGY 


281 


Pulaski   and  Wythe   Counties,   Virginia;   Colorado;   Utah;   Tennessee; 
Arkansas. 

Hemimorphite  is  an  important  ore  of  zinc. 


Andalusite  Group 

The  compound  Al2Si05  is  trimorphous  and  occurs  in  nature  as  the 
three  minerals  andalusite,  sillimanite,  and  cyanite.  The  first  two  min- 
erals crystallize  in  the  orthorhombic  system,  while  the  third  is  triclinic. 
Andalusite  and  sillimanite  are  very  closely  related  in  many  respects,  and 
are  considered  salts  of  the  orthosilicic  acid.  Cyanite  is  thought  to  be 
derived  from  the  metasilicic  acid. 


FIG.  581. — Andalusite.     An- 
dalusia,   Spain. 


ANDALUSITE,  Al2SiO5 

Orthorhombic,  bipyramidal  class.  Occurs  usually  in  large,  rough, 
and  nearly  square  prismatic  crystals  (Figs.  580  and  581).  Chiastolite 
is  a  variety  with  a  regular  internal  arrangement  of  dark  organic  matter, 


FIG.  582. — Andalusite:  Variety,  chiastolite.     Lancaster,  Massachusetts. 

best  seen  in  polished  cross-sections  (Fig.  582) .  Found  also  in  fibrous, 
columnar,  and  granular  masses,  and  in  rounded  pebbles. 

Prismatic  cleavage.  Uneven  fracture.  Hardness  7  to  7.5,  due  to 
alteration  may  be  softer  on  the  surface.  Specific  gravity  3.1  to  3.2. 
Gray,  greenish,  reddish,  or  bluish  in  color.  Transparent  to  opaque. 
Vitreous  to  dull  luster.  Sometimes  strongly  pleochroic. 

Al2SiO5.  Often  impure.  Infusible.  Insoluble  in  acids.  Alters  to 
cyanite,  mica,  kaolinite,  or  dense  talcose  minerals  resembling  steatite. 

Occurs  in  metamorphic  rocks,  especially  in  schists  and  slates.     Com- 


282  MINERALOGY 

monly  associated  with  cyanite,  sillimanite,  mica,  garnet,  and  tourmaline. 
Some  localities  are:  Andalusia,  Spain;  Tyrol;  in  transparent  crystals  in 
Minas  Gerses,  Brazil;  Ceylon;  Westford,  Lancaster,  and  Sterling,  Massa- 
chusetts; Litchfield  and  Washington,  Connecticut;  Standish,  Maine; 
Madera  County,  California. 

Transparent  varieties  are  sometimes  used  for  gem  purposes. 

Sillimanite  (Fibrolite),  Al2SiO5. 

Orthorhombic.  Usually  in  long,  thin,  needle-like  crystals;  or  in 
radiating  fibrous  or  columnar  masses.  Crystals  are  often  bent,  striated, 
interlaced,  poorly  terminated,  and  without  sharp  edges. 

Macropinacoidal  cleavage.  Uneven  fracture.  Hardness  6  to  7. 
Specific  gravity  3.2  to  3.3.  Gray,  brown,  yellowish,  or  greenish  in  color. 
Vitreous  or  silky  luster.  Transparent  to  translucent. 

Al2SiO5.  Chemical  composition  and  behavior 
are  the  same  as  for  andalusite. 

Occurs  as  an  accessory  constituent  of  gneisses, 
quartzites,  mica  schists,  and  other  metamorphic 
rocks.  It  is  sometimes  associated  with  andalu- 
site, zircon,  or  corundum.  Found  at  Boden- 
mais,  Bavaria;  Freiberg,  Saxony;  Minas  Geraes, 
Brazil;  Worcester,  Massachusetts;  Norwich  and 
Willimantic,  Connecticut;  Westchester  and  Mon- 
roe counties,  New  York;  Chester,  Pennsylvania. 

CYANITE  (Disthene,  Kyanite),  Al2SiO5). 

FIG.  583.  — Cyanite  Triclinic,  prismatic  class.  Generally  in  long, 
Litchfield'Con-  broad  crystals  without  distinct  terminations;  or 
in  coarse  bladed,  columnar,  or  fibrous  masses 
(Fig.  583).  Crystals  are  sometimes  curved  and  arranged  radially. 

Macro-  and  brachypinacoidal  cleavages.  Hardness  varies  greatly 
with  direction,  4  to  5  parallel  to  the  long  direction  of  the  blades,  6  to  7 
across  them.  Specific  gravity  3.5  to  3.7.  Generally  some  shade  of  blue 
in  color;  also  grayish,  white,  green,  brownish,  or  colorless.  The  edges 
are  usually  lighter  in  color  than  the  central  portions  of  the  blades,  that 
is,  the  color  is  distributed  in  streaks  or  spots.  Vitreous  luster.  Trans- 
parent to  translucent. 

Al2SiO5.  Chemical  composition  and  behavior  similar  to  that  of 
andalusite  and  sillimanite.  Cyanite  is,  however,  more  resistive  to  the 
action  of  acids. 

Cyanite  is  a  metamorphic  mineral  and  is  commonly  found  in  gneisses 
and  mica  schists,  especially  paragonite  schist.  Usual  associates  are 
staurolite,  garnet,  corundum,  rutile,  and  lazulite.  Some  localities 
are:  the  Saint  Gothard  district,  Switzerland;  various  places  in  Tyrol; 
Sweden;  Brazil;  Chesterfield,  Massachusetts;  Litchfield  and  Washington, 


DESCRIPTIVE  MINERALOGY 


283 


Connecticut;   Chester    and  Delaware   counties,   Pennsylvania;  Gaston, 
Rutherford,  and  Yancey  counties,  North  Carolina. 
Sometimes  used  for  gem  purposes. 


TOPAZ,  Al2(F,OH)2Si04. 

Orthorhombic,  bipyramidal  class.  Generally  in  highly  modified, 
prismatic  crystals,  which  are  usually  developed  on  one  end  only  (Figs. 
584,  585  and  586).  Often  vertically  striated.  Occurs  also  in  granular 
to  compact  masses,  and  in  rolled  fragments. 

Very  perfect  basal  cleavage.  Conchoidal  to  uneven  fracture.  Hard- 
ness 8.  Specific  gravity  3.4  to  3.6.  Colorless,  wine  yellow,  grayish, 
violet,  reddish,  or  bluish  in  color.  Some  colored  varieties  fade  on  expo- 
sure to  sunlight.  Transparent  to  opaque.  Vitreous  luster. 

Al2(F,OH)2SiO4.  The  percentages  of  fluorine  and  hydroxyl  vary 
greatly.  Infusible.  Slightly  acted  upon  by  sulphuric  acid.  Sometimes 
alters  to  talc  and  kaolinite. 


FIG.  584. 


FIG.  585. 


FIG.  586. 


Topaz  is  a  characteristic  mineral  of  the  pneumatolytic  process  of 
formation  and  is  hence  generally  associated  with  cassiterite,  tourmaline, 
quartz,  fluorite,  apatite,  beryl,  mica,  scheelite,  wolframite,  and  zircon. 
It  occurs  in  crevices,  cavities,  and  pegmatite  dikes  in  highly  acid  igneous 
rocks  such  as  granites,  rhyolites,  gneisses,  and  mica  schists.  Excellent 
crystals  are  found  at  Schneckenstein  and  elsewhere  in  Saxony;  Ural 
Mountains;  Sweden;  Japan;  Australia;  Mexico;  Thomas  Range,  Utah; 
Nathrop,  Colorado;  San  Diego  County,  California;  and  various  places 
in  Connecticut,  New  Hampshire,  and  Maine.  Frequently  found  in  the 
sands  and  gravel  of  the  streams  of  Ceylon,  Brazil,  and  the  Ural 
Mountains. 

Clear  and  transparent  crystals  are  used  for  gem  purposes.  The 
yellow  variety  from  Brazil  is  often  called  precious  topaz. 

Datolite,  Ca(B.OH)SiO4. 

Monoclinic,  prismatic  class.  Usually  prismatic,  pyramidal,  or  tabular 
crystals,  often  highly  modified  (Figs.  587  and  588).  Also  in  compact, 


284  MINERALOGY 

dull,  or  granular  masses  resembling  wedgewood  ware  or  unglazed  porcelain 
(Fig.  589). 

Conchoidal  to  uneven  fracture.  Hardness  5  to  5.5.  Specific  gravity 
2.9  to  3.  Colorless,  white,  or  greenish,  but  often  with  yellowish,  reddish, 
or  brownish  streaks  and  spots.  Transparent  to  translucent,  rarely 
opaque.  Vitreous  to  dull  luster. 

Ca(B.OH)Si04.  Crystals  are  usually  very  pure.  Gelatinizes  with 
hydrochloric  acid. 

Datolite  is  a  secondary  mineral  and  is  generally  found  in  cracks  and 
cavities  in  basic  igneous  rocks,  such  as  diorite,  diabase,  melaphyre,  gabbro, 
and  serpentine.  The  common  associates  are  native  copper,  calcite, 
epidote,  magnetite,  and  the  zeolites.  Some  localities  are:  the  Kil- 
patrick  Hills,  Scotland;  Arendal,  Norway;  Hartz  Mountains;  Tyrol; 


FIG.  587. 


FIG.  588.  FIG.    589.— Datolite.     Lake  Superior 

Copper  District. 

Bergen  Hill,  New  Jersey;  Westfield  and  elsewhere,  Massachusetts; 
Hartford,  Connecticut;  in  the  Lake  Superior  copper  district  excellent 
crystals  and  compact  porcelain-like  masses. 

The  massive  varieties  are  sometimes  used  for  gem  purposes. 

TOURMALINE,  H2oB2Si4O2i. 

Hexagonal,  ditrigonal  pyramidal  class.  Commonly  in  short  to 
long  prismatic  crystals  with  vertical  striations.  Well-developed  crystals 
have  rhombohedral-like  terminations  and  possess  pronounced  hemimor- 
phism  (Figs.  590,  and  591).  Crystals  show  a  characteristic  spherical 
triangular  outline  in  cross-section  (Figs.  592  and  593).  Occurs  also  in 
compact  and  disseminated  masses,  and  in  radially  divergent  aggregates, 
called  tourmaline  suns;  also  in  loose  crystals  in  secondary  deposits. 

Conchoidal  to  uneven  fracture.  Hardness  7  to  7.5.  Specific  gravity 
2.9  to  3.2.  Usually  pitch  black  or  brown  in  color;  also  gray,  yellovv, 
green,  or  red,  and  more  rarely  colorless  or  white.  The  reddish  varieties 
are  frequently  called  rubellite.  Zonal  distribution  of  color  is  often  very 


DESCRIPTIVE  MINERALOGY 


285 


marked,  especially  in  crystals  of  the  lighter  colors  (Fig.  593).  Vitreous 
to  resinous  luster.  Transparent  to  opaque.  Strongly  dichroic,  and 
often  pyroelectric. 

H2oB2Si4O2i.  A  very  complex  silicate  with  varying  amounts  of  iron, 
aluminum,  magnesium,  manganese,  calcium,  lithium,  sodium,  potassium, 
hydroxyl,  and  fluorine.  Sometimes  classified  according  to  composition 
as  lithium,  iron,  and  magnesium  tourmalines.  Fusibility  varies  greatly. 


FIG.  590. 


FIG.  591. 


FIG.  592. 


Insoluble  in  acids,  but  gelatinizes  after  fusion  or  strong  ignition.     Alters 
to  muscovite,  biotite,  or  chlorite. 

Tourmaline  is  a  very  characteristic  mineral  of  pegmatite  dikes  as- 
sociated with  intrusions  of  granite.  It  is  the  result  of  pneumatolytic 
action  as  is  evidenced  by  the  presence  of  fluorine,  hydroxyl,  and  boron. 
It  is  also  rather  common  in  metamorphic  rocks,  such  as  gneisses,  schists, 
and  in  crystalline  limestones  and  dolomites.  Some  of  the  common 


FIG.  593. — Tourmaline  showing 
zonal  distribution  of  color  and  spheri- 
cal triangular  outline.  San  Diego 
County,  California. 


FIG.  594. — Tourma-  FIG.      595. — Tourma- 

line  in    quartz.       Au-     line   in    albite.         Mesa 
burn,  Maine.  Grande,  California. 


associates  are  quartz  (Fig.  594),  feldspar  (Fig.  595),  beryl,  topaz,  fluorite, 
lepidolite  (Fig.  596),  apatite,  and  muscovite.  Excellent  crystals  occur 
on  the  Island  of  Elba;  in  Ural  Mountains;  Burma;  Ceylon;  Madagascar; 
Minas  Geraes,  Brazil;  Paris,  Auburn,  and  Rumford,  Maine;  Haddam 
Neck,  Connecticut;  Gouverneur  and  elsewhere  in  Saint  Lawrence  County, 
New  York;  Mesa  Grande,  Pala,  and  elsewhere  in  San  Diego  County, 
California. 


286 


MINERALOGY 


Stones  of  good  colors  are  used  for  gem  purposes.  On  account  of  its 
strong  absorption  of  light  it  has  been  used  in  the  making  of  tourmaline 
tongs,  a  simple  instrument  for  the  production  of  polarized  light. 


PIG.  596. — Tourmaline:  Variety,  rubellite,  in  lepidolite.     San  Diego  County,  California. 

Chondrodite  [Mg(F,OH)]2Mg3(SiO4)2. 

Monoclinic,  prismatic  class.  Occurs  in  small,  highly  modified, 
pseudo-orthorhombic  crystals,  also  in  grains  or  lumps,  and  in  granular 
aggregates. 

Basal  cleavage.  Uneven  to  conchoidal  cleavage.  Hardness  6  to 
6.5.  Specific  gravity  3.1  to  3.3.  Brown,  yellow,  or  red  in  color. 
Vitreous  to  resinous  luster.  Translucent  to  opaque. 

[Mg(F,OH)]2Mg3(SiO4)2.  Some  of  the  magnesium  may  be  replaced 
by  bivalent  iron.  Infusible.  Gelatinizes  with  hydrochloric  acid.  Alters 
to  serpentine  and  brucite. 

Chondrodite  is  a  typical  contact  metamorphic  mineral.  It  occurs 
commonly  in  crystalline  limestones  and  dolomites,  associated  with  spinel, 
vesuvianite,  magnetite,  pyroxene,  and  phlogopite.  Some  important 
localities  are:  Pargas,  Finland;  Mount  Vesuvius;  Burma;  Sparta,  New 
Jersey;  Tilly  Foster  mine,  near  Brewster,  and  in  Orange  County,  New 
York. 

Epidote  Group 

Under  this  heading  two  rather  complex  but  isomorphous  silicates 
of  calcium  and  aluminum  will  be  described. 

EPIDOTE,  Ca2(Al,Fe)2(A1.0H)(Si04)3. 

Monoclinic,  prismatic  class.  Excellent  prismatic  and  highly  modified 
crystals  are  rather  common;  usually  elongated  and  deeply  striated  parallel 
to  the  b  axis,  and  terminated  at  one  end  only  (Figs.  597  and  598).  Occurs 
also  in  divergent  or  parallel  fibrous  and  columnar  aggregates,  coarse  to 
fine  granular  masses,  or  in  rounded  or  angular  grains. 

Basal  cleavage.  Uneven  fracture.  Hardness  6  to  7.  Specific 
gravity  3.3  to  3.5.  Yellowish  to  blackish  green  in  color;  more  rarely 
red  or  colorless.  Crystals  are  usually  darker  in  color  than  massive  varie- 
ties. Vitreous  to  resinous  luster.  Transparent  to  opaque.  Strongly 
pleochroic. 


DESCRIPTIVE  MINERALOGY 


287 


Ca2(Al,Fe)2(ALOH)  (SiO4)  3.  The  percentages  of  the  oxides  of  calcium, 
iron,  aluminum,  and  silicon  vary  considerably.  Clinozoisite  contains 
little  or  no  iron.  Zoisite  is  an  orthorhombic  modification.  Loses  water 
when  strongly  ignited,  and  gelatinizes  with  hydrochloric  acid  after 
ignition.  Occurs  as  a  pseudomorph  after  scapolite,  garnet,  augite,  and 
hornblende. 

Epidote  is  a  typical  metamorphic  mineral.  It  is  found  in  such  rocks 
as  gneiss,  and  schists  of  various  kinds;  often  occurs  very  extensively, 
forming  epidote  rocks  and  schists.  It  is  commonly  associated  with  garnet, 
vesuvianite,  hornblende,  hematite,  native  copper,  magnetite,  and  the 
zeolites.  It  is  also  a  common  alteration  product  of  minerals  high  in 
calcium  and  aluminum,  such  as  feldspar,  pyroxene,  amphibole,  scapolite, 
and  biotite.  Important  localities  are:  Zillerthal  and  Untersulzbachthal, 
Tyrol;  Travesella,  Piedmont;  Island  of  Elba;  Dauphine,  France;  Arendal, 
Norway;  Ural  Mountains;  Haddam,  Connecticut;  various  places  in  New 


FIG.  597. 


FIG.  598. — Epidote.     Untersulzbachthal, 
Tyrol. 


York,  New  Jersey,  and  Colorado ;  with  native  copper  in  the  Lake  Superior 
copper  district. 

The  clear  and  transparent  dark  green  crystals  are  sometimes  used  for 
gem  purposes. 

Orthite  (Attanite),  Ca2(Al,Ce,Fe)2(Al.OH)(SiO4)3. 

Monoclinic,  prismatic  class.  Crystals  are  tabular  or  prismatic,  but 
rare.  Usually  in  massive,  granular,  or  bladed  aggregates;  also  as  dis- 
seminated grains. 

Uneven  to  conchoidal  fracture.  Hardness  5.5  to  6.  Specific 
gravity  3  to  4.  Pitch  black  in  color,  sometimes  brownish  or  grayish; 
often  coated  with  a  yellowish  or  brownish  alteration  product.  Greenish 
gray  to  brown  streak.  Pitchy  submetallic  luster.  Opaque. 

Ca2(Al,Ce,Fe)2(A1.0H)(SiO4)3.  Composition  varies  greatly.  Didym- 
ium,  lanthanum,  yttrium,  magnesium,  and  water  may  be  present. 
Fuses  easily  with  intumescence  to  a  black  magnetic  glass.  Gelatinizes 
with  hydrochloric  acid,  but  not  if  previously  ignited. 

Orthite  occurs  in  small  quantities  in  igneous  rocks,  such  as  granites 
and  pegmatites;  also  in  gneiss,  mica  and  amphibolite  schists,  and  crystal- 
line limestones.  Commonly  associated  with  epidote,  magnetite,  quartz, 


288 


MINERALOGY 


and  feldspar.  Occurs  in  Greenland;  Falun,  Sweden;  Miask,  Ural  Moun- 
tains; Edenville,  New  York;  Haddam,  Connecticut;  Franklin,  New 
Jersey;  Madison  and  Iredell  counties,  North  Carolina;  Barringer  Hill, 
Texas;  Amherst  County,  Virginia. 


VESUVIANITE  (Idocrase),  Ca6[Al(OH,F)]Al2(SiO4)5. 

Tetragonal,  ditetragonal  bipyramidal  class.     Crystals  are  generally 
short  prismatic  (Figs.  599,  600,  and  601),  rarely  pyramidal  or  acicular. 
Occurs  also  in  compact  and  granular  masses,  and  in  ag- 
gregates with  parallel  or  divergent  striations  or  furrows. 
Uneven  fracture.     Hardness  6.5.     Specific  gravity 
3.3  to  3.5.     Occurs  in  many  shades  of  yel-low,  green, 
and   brown;    mpre   rarely   blue,   red,  or  nearly  black. 
Calif ornite  is  a  compact  green  variety  with  colorless  or 
white  streaks,  resembling  jade.     Vitreous  greasy  luster. 
Commonly  translucent. 

Ca6[Al(OH,F)]Al2(SiO4)5.  The  composition  is  com- 
plex and  variable.  May  contain  titanium,  boron,  iron,  magnesium,  man- 
ganese, sodium,  potassium,  and  lithium.  Fuses  with  intumescence  to 
a  greenish  or  brownish  glass.  After  ignition,  it  decomposes  easily  with 
acids. 

Vesuvianite  is  a  typical  contact  metamorphic  mineral.     It  is  found 
commonly  in  crystalline  limestones,  gneiss,  and  schists,  associated  with 


FIG.  599. 


FIG.  600. — Vesuvianite.     (a)  Wilui  River, 
Siberia;  (6)  Achmatovsk,  Russia. 


FIG.    601.— Vesuvianite. 
Tyrol. 


Fassathal, 


garnet,  tourmaline,  chondrodite,  wollastonite,  epidote,  and  the  pyroxenes. 
Important  localities  are:  Monzoni,  Tyrol;  Ala  Valley,  Piedmont; 
Vesuvius;  Morelos,  Mexico;  Eger,  Hungary;  Wilui  River,  Siberia; 
Rumford,  Maine;  Amity,  New  York;  various  places  in  California, 
Ontario,  and  Quebec. 

Clear  and  transparent  brown  and  green  varieties  are  used  for  gem 
purposes. 


DESCRIPTIVE  MINERALOGY 


289 


Olivine  Group 

This  group  contains  minerals  which  are  normal  orthosilicates.  Only 
two  members  of  the  group  occur  abundantly  enough  to  be  described. 

OLIVINE  (Chrysolite,  Peridot),  (Mg,Fe)2SiO4. 

Orthorhombic,  bipyramidal  class.  Crystals  are  prismatic  (Fig. 
602)  or  thick  tabular.  Occurs  generally  in  rounded,  disseminated, 
glassy  grains  (Fig.  603),  granular  aggregates,  or  in  rounded  loose  pebbles. 

Pinacoidal  cleavages.  Conchoidal  fracture.  Hardness  6.5  to  7. 
Specific  gravity  3.2  to  3.6.  Vitreous  luster.  Commonly  various  shades 
of  green,  also  yellowish,  brown,  reddish,  grayish,  or  colorless.  Trans- 
parent to  translucent. 

(Mg,Fe)2SiO4.  The  composition  varies  between  that  of  forsterite, 
Mg2SiO4,  and  fayalite,  Fe2Si04.  Titanium,  nickel,  and  calcium  may  be 
present  in  small  amounts.  Infusible.*  Easily  decomposed  and  gela- 


FIG.  602. 


FIG.  603. — Olivine  (green  glassy  grains). 
Near  Balsam,  North  Carolina. 


tinizes  with  acids.  Alters  to  serpentine,  limonite,  magnesite,  opal,  and 
garnierite. 

Olivine  is  a  constituent  of  many  basic  igneous  rocks,  such  as  basalt, 
gabbro,  and  peridotite.  Found  also  in  crystalline  limestones.  The  com- 
mon associates  are  augite,  enstatite,  spinel,  plagioclase,  chromite, 
pyrope,  corundum,  talc,  and  magnetite.  Occurs  in  northern  Egypt; 
Mount  Vesuvius;  Upper  Burma;  Snarum,  Norway;  Arizona;  Vermont; 
New  Hampshire ;  Virginia ;  Pennsylvania ;  Oregon ;  New  Mexico ;  Canada ; 
Brazil. 

Peridot  is  a  transparent  green  variety  used  for  gem  purposes. 

Willemite,  Zn2SiO4. 

Hexagonal,  trigonal  rhombohedral  class.  Crystals  are  either  slender 
or  thick  prismatic  in  habit,  but  generally  quite  small.  Troostite,  a 
variety  containing  manganese,  is  commonly  found  in  larger  crystals. 
Occurs  also  in  compact,  or  granular  masses,  and  in  disseminated  grains 
(Fig.  604). 

Basal  Cleavage.  Uneven  fracture.  Hardness  5  to  6.  Fracture 
3.9  to  4.3.  Greasy  vitreous  luster.  Commonly  yellow,  green,  brown,  or 

19 


290 


MINERALOGY 


reddish;  more  rarely  blue,  black,  white,  or  colorless.  Transparent  to 
opaque. 

Zn2SiO4.  Manganese  and  iron  may  be  present.  Fuses  with  diffi- 
culty. Gelatinizes  with  hydrochloric  acid.  Sometimes  pseudomorphous 
after  calamine. 

The  usual  associates  are  franklinite,  zincite,  rhodonite,  and  calcite. 
The  most  important  locality  is  Franklin  Furnace  and  vicinity,  Sussex 
County,  New  Jersey,  where  it  occurs  in  large  quantities.  Found  also  at 
Altenberg,  near  Aachen,  Germany;  Musartut,  Greenland;  Merritt  Mine, 
Socorro  County,  New  Mexico;  and  Clifton,  Arizona. 

Willemite  is  an  important  ore  of  zinc. 


FIG.  604.  —  Willemite  (light)  with  Franklinite.     Franklin  Furnace,  New  Jersey. 

Garnet  Group 

This  group  embraces  minerals  possessing  the  general  formula,R"3R'"2 
(Si04)3,  in  which  R"  may  be  calcium,  magnesium,  manganese,  or  ferrous 
iron,  and  R"  '  aluminum,  ferric  iron,  or  chromium.  Sometimes  titanium 
may  replace  a  portion  of  the  silicon.  Six  varieties  depending  upon  com- 
position have  been  distinguished. 

Grossularite  ..................................  Ca3Al2(SiO4)3 

Pyrope  ......................................  Mg3Al2(SiO4)s 

Spessartite  ...................................  Mn3Al2(SiO4)3 

Almandite  ...................................  Fe3Al2(SiO4)3 

Uvarovite  .............................    ......  Ca3Cr2(SiO4)3 

Andradite  ....................................  Ca. 


These  varieties  grade  over  into  one  another,  the  composition  of  a 
given  specimen  being  usually  rather  complex. 

Cubic,  hexoctahedral  class.  Crystals  are  usually  rhombic  dodeca- 
hedrons or  tetragonal  trisoctahedrons,  often  in  combination  (Figs. 
605  to  609).  The  hexoctahedron  is  quite  frequently  observed  (Fig. 


DESCRIPTIVE  MINERALOGY 


291 


607).  Other  forms  are  rare.  Generally  well  crystallized,  but  occurs 
also  as  rounded  disseminated  glassy  grains,  and  in  compact  granular 
aggregates. 

Indistinct  dodecahedral  cleavage.  Conchoidal  to  uneven  fracture. 
Hardness  6.5  to  7.5.  Specific  gravity  3.4  to  4.3,  varying  with  the  com- 
position. Commonly  red,  brown,  yellow,  green,  or  black;  less  frequently 


FIG.  605. — Garnet  (rhombic 
dodecahedron).  Salida,  Colo- 
rado. 


FIG.  606. 


FIG.  607. 


white  or  colorless.  Light  colored  garnets  are  generally  transparent  to 
translucent,  dark  colored  varieties  translucent  to  opaque.  Vitreous  to 
resinous  luster. 

R"3R" '2(8^4)3.  Composition  varies  greatly  as  indicated  above. 
The  chemical  properties  of  the  six  varieties  differ  materially.  They 
generally  fuse  easily  to  a  brownish  or  black  glass,  which  is  sometimes  mag- 


FIG.  608. 


FIG.  609. — Garnet   (tetragonal    trisoctahedrons) 
in   mica   schist.     Sunday   River,    Maine. 


netic.  With  the  exception  of  uvarovite,  all  varieties  gelatinize  with  acids 
after  fusion.  Garnets  alter  readily;  epidote,  mica,  chlorite,  serpentine, 
hornblende,  scapolite,  orthoclase,  calcite,  and  limonite  have  been  ob- 
served occurring  as  pseudomorphs  after  garnet.  Large  chlorite  pseudo- 
morphs  after  garnet  occur  at  Spurr  Mountain  Mine,  Lake  Superior  region. 
Garnet  is  a  very  common  mineral.  It  occurs  in  crystalline  schists, 


292  MINERALOGY 

as  a  contact  metamorphic  mineral,  as  a  constituent  of  many  eruptive 
rocks,  with  various  ores,  and  in  secondary  deposits. 

Grossularite,  Hessonite,  Cinnamon  Stone. — Calcium-aluminum  gar- 
net. Calcium  may  be  partially  replaced  by  ferrous  iron,  and  aluminum 
by  ferric  iron.  Specific  gravity  varies  from  3.4  to  3.7.  White,  various 
shades  of  yellow,  cinnamon  brown,  rose  red;  also  green  and  colorless.  It 
occurs  in  crystalline  limestones  and  dolomites  with  wollastonite,  vesuvia- 
nite,  diopside,  and  scapolite.  Some  localities  are:  Ceylon;  Mussa  Alp, 
Piedmont;  Wilui  River,  Siberia;  Morelos,  Mexico;  Monzoni,  Tyrol; 
Rumford,  Maine;  Warren,  New  Hamsphire.  Yellow  and  orange  grossu- 
larites  are  used  for  gem  purposes. 

Pyrope. — Magnesium-aluminum  garnet.  Calcium  and  ferrous  iron 
may  partially  replace  magnesium.  Specific  gravity  3.7.  Deep  red  to 
almost  black.  When  clear  and  transparent  is  often  called  precious 
garnet  and  used  as  a  gem.  Commonly  known  as  Cape  ruby  or  Arizona 
ruby.  Found  usually  in  basic  igneous  rocks,  such  as  peridotite  or  serpen- 
tine. Frequently  considered  an  important  associate  of  the  diamond. 
Rarely  found  in  good  crystals,  usually  in  irregular  particles  or  rounded 
grains.  Important  localities  are  Teplitz,  Aussig,  and  Bilin,  Bohemia; 
Kimberley  and  other  diamondiferous  localities  in  South  Africa;  various 
places  in  Arizona  and  New  Mexico. 

Spessartite. — Manganese-aluminum  garnet.  May  contain  ferrous 
and  ferric  iron.  Specific  gravity  4  to  4.3.  Brownish  to  hyacinth  red. 
Occurs  in  granitic  rocks  with  topaz,  tourmaline,  quartz,  and  orthoclase. 
Occurs  in  Tyrol;  Piedmont;  Ceylon;  Haddam,  Connecticut;  Amelia 
Court  House,  Virginia;  Bethel,  Maine;  Salem,  North  Carolina. 

Almandite,  Carbuncle. — Iron-aluminum  garnet.  May  contain  mag- 
nesium and  ferric  iron.  Specific  gravity  3.9  to  4.2.  Deep  red  to  brown- 
ish red  or  black  in  color.  Transparent  red  varieties  are  known  as 
precious  garnets  and  used  as  gems;  translucent  varieties  are  called  common 
garnets.  Commonly  found  in  mica  and  other  schists,  associated  with 
staurolite,  cyanite,  andalusite,  and  tourmaline.  Excellent  specimens  are 
obtained  in  India;  Ceylon;  Minas  Novas,  Brazil;  Bodo,  Norway;  Tyrol; 
Uruguay;  Australia;  Salida,  Colorado;  Fort  Wrangel,  Alaska;  Charle- 
mont,  Massachusetts.  Rhodolite  is  a  pale  violet  variety,  between  pyrope 
and  almandite,  occurring  in  Macon  County,  North  Carolina. 

Uvarovite. — Calcium-chromium  garnet.  Emerald  green  in  color. 
Crystals  are  usually  small.  Not  a  common  variety.  Found  with 
chromite  in  serpentine  or  in  crystalline  limestones  and  gneiss.  Some 
localities  are  Ural  Mountains;  Oxford,  Canada;  New  Idria,  California. 
Andradite. — Calcium-iron  garnet.  The  composition  varies  greatly. 
The  color  may  be  brownish  red,  brown,  grayish  black,  black,  also  various 
shades  of  yellow  or  green.  Topazolite  is  yellowish  or  greenish,  and  often 
resembles  topaz.  Demantoid  is  a  grass  green  variety.  Melanite  is  black. 


DESCRIPTIVE  MINERALOGY  293 

These  garnets  occur  in  syenite,  serpentine,  chloritic  schists,  and  crystal- 
line limestones.  Common  associates  are  feldspar,  nephelite,  leucite, 
epidote,  and  magnetite.  Found  at  Dobschau,  Hungary;  Tyrol;  Island 
of  Elba;  Arendal,  Norway;  Ural  Mountains;  Franklin,  New  Jersey; 
Magnet  Cove,  Arkansas;  Henderson,  North  Carolina. 

Pyrope  and  almandite  furnish  most  of  the  garnets  used  as  gems. 
Almandite  and  andradite  are  often  called  common  garnets.  Small 
garnets  are  sometimes  used  as  jewels  in  watches  of  a  cheaper  grade. 
Massive  and  compact  garnet  is  used  as  an  abrasive  and  for  making  sand- 
paper. In  1916,  6,171  short  tons  of  garnet  were  produced  in  the  United 
States  for  abrasive  purposes. 


CHRYSOCOLLA,  CuO,  SiO2,  H2O. 

Usually  apparently  amorphous.  Tetragonal  or  hexagonal.  Crystals 
are  small,  acicular,  and  very  rare.  Occurs  in  compact,  reniform,  or 
earthy  masses;  also  as  incrustations  and  stains,  and  in  veins.  May  have 
an  enamel-like  appearance  and  resemble  opal. 

Conchoidal  fracture.  Hardness  2  to  4.  Specific  gravity  2  to  2.2. 
Usually  various  shades  of  green  or  blue;  when  impure,  brown  to  black. 
Translucent  to  opaque.  Vitreous,  greasy,  or  dull  luster. 

Chemically  chrysocolla  is  considered  a  solid  solution  of  CuO,  Si02, 
and  H2O  in  varying  proportions.  Infusible.  Decomposed  by  acids 
but  does  not  gelatinize.  Forms  pseudomorphs  after  atacamite,  azurite, 
and  cerussite. 

Chrysocolla  is  a  secondary  mineral,  formed  by  the  alteration  of  various 
copper  ores,  such  as  chalcopyrite,  cuprite,  and  tetrahedrite.  Generally 
found  in  the  zone  of  oxidation  of  copper  deposits.  It  is  commonly  as- 
sociated with  malachite,  native  copper,  azurite,  and  limonite.  Some 
localities  are:  Cornwall,  England;  Ural  Mountains;  Clifton  and  Bisbee 
copper  districts,  Arizona;  Wyoming;  Nevada;  New  Mexico;  Lake  Superior 
copper  district;  in  fact  all  important  copper  localities. 

It  is  an  ore  of  copper.  It  is  sometimes  cut  and  polished  for  gem 
purposes.  At  times  it  is  substituted  for  turquois. 

Mica  Group 

Although  the  members  of  the  mica  group  vary  greatly  from  the 
chemical  standpoint,  they  have,  nevertheless,  many  characteristics 
in  common.  Crystals  are  apparently  hexagonal  or  orthorhombic  in  de- 
velopment, but  they  all  belong  to  the  monoclinic  system.  The  prism 
angle  usually  approximates  120°.  Twins  are  not  uncommon.  The  micas 
possess  an  excellent  basal  cleavage,  which  is  sometimes  considered  the 
most  perfect  cleavage  to  be  observed  on  minerals.  Cleavage  laminae 
are  elastic. 

The  micas  are  silicates  of  varying  compositions  of  aluminum  and 


294  MINERALOGY 

potassium,  containing  hydrogen,  magnesium,  iron,  sodium,  lithium, 
and  fluorine.  The  silica  content  varies  between  33  per  cent,  and  55  per 
cent.  Several  theories  have  been  advanced  to  explain  the  rather  com- 
plex composition  of  the  members  of  this  group.  According  to  Clarke, 
the  micas  are  derived  from  the  hypothetical  orthosilicate  Al4(SiO4)3, 
while  Tschermak  considers  them  as  mixtures  in  varying  proportions  of 
H3Al3(Si04)3  and  (Mg,Fe)6  (SiO4)3. 

The  following  four  varieties  occur  extensively,  and  are  to  be  considered 
among  the  most  common  and  important  minerals. 

Biotite,  (K,H)2(Mg,Fe)2(Al,Fe)2(Si04) ,. 

Phlogopite,  (K,H)3Mg3Al(SiO4)3. 

Muscovite,  H2KAl3(SiO4)3. 

Lepidolite,  (Li,K)  2 (F, OH)  2Al2Si 3O9. 

All  of  the  micas  yield  water  when  heated  in  a  closed  tube.  They  fuse 
with  difficulty.  They  are  important  rock  forming  minerals,  being  es- 
sential constituents  of  many  igneous  and  metamorphic  rocks.  Some 
sedimentary  rocks  often  contain  considerable  quantities  of  mica. 

BIOTITE  (Magnesium-iron  Mica,  Black  Mica),  (K,H)2(Mg,Fe)2(Al,Fe)2- 
(Si04)3. 

Monoclinic,  prismatic  class.     Crystals  are  usually  tabular  with  an 
hexagonal  (Fig.  610)  or  rhombohedral  habit;  sometimes  striated  horizon- 
tally.    Crystals   are  rare.     Generally  found  in 
plates,  lamellar  masses,  or  disseminated  scales. 
Highly  perfect  basal  cleavage.     Hardness  2.5 
to  3.     Specific  gravity  2.7  to  3.2.     Dark  brown 
or  black  in  color;  more  rarely,  light  brown,  or 
FIG.  6io.  greenish.     White    to    greenish    streak.     Trans- 

parent to  opaque.  Sometimes  shows  asterism. 
(K,H)2(Mg,Fe)2(Al,Fe)2(Si04)3.  The  composition  varies  greatly. 
May  contain  titanium,  sodium,  and  fluorine.  Lepidomelane  contains 
large  amounts  of  the  oxides  of  iron  and  but  little  MgO.  Fuses  with 
difficulty.  Only  slightly  attacked  by  hydrochloric  acid;  completely 
decomposed  by  hot  concentrated  sulphuric  acid.  Alters  to  chlorite, 
or  to  epidote,  quartz,  and  iron  oxide. 

Biotite  is  an  extremely  common  mica,  being  an  important  constituent 
of  many  igneous  and  metamorphic  rocks,  such  as,  granite,  syenite, 
diorite,  porphyry,  gneiss,  and  mica  schists.  It  is  often  associated  with 
muscovite. 

Biotite  is  of  little  use  commercially. 

Phlogopite    (Magnesium    Mica,  Amber    Mica,   Bronze    Mica),    (K,H)3- 

Mg3Al(Si04)3. 

Monoclinic,  prismatic  class.  Crystals  usually  resemble  those  of 
biotite  in  form  and  habit,  and  are  sometimes  large  and  coarse  (Fig.  611). 


DESCRIPTIVE  MINERALOGY 


295 


They  may  be  hexagonal  or  orthorhombic  in  outline.     Commonly  found 
in  disseminated  scales,  plates,  or  aggregates. 

Highly  perfect  basal  cleavage.  Thin  laminae  are  tough  and  elastic. 
Specific  gravity  2.8  to  3.  Pearly  to  submetallic  luster.  Color  may  be 
silvery  gray,  yellow,  brown,  green,  copper  or  bronze  red.  Thin  leaves 
are  transparent.  Often  shows  asterism. 

(K,H)3Mg3Al(SiO4)3.  Usually  contains  small 
amounts  of  iron,  sodium,  and  fluorine.  Whitens 
and  fuses  on  thin  edges.  Slightly  acted  upon  by 
hydrochloric  acid,  but  readily  decomposed  by  hot 
concentrated  sulphuric. 

Phlogopite  occurs  in  crystalline  limestones, 
dolomites,  schists,  and  in  serpentine.  Important 
localities  are:  Pargas,  Finland;  Aeker,  Sweden; 
Fassathal,  Tyrol;  St.  Lawrence  and  Jefferson 
counties,  New  York;  Morris  and  Warren  counties, 
New  Jersey;  Sydenham  and  Burgess,  Ontario, 
where  crystals  measuring  seven  feet  across  the 
cleavage  plane  have  been  found;  various  locali- 
ties in  Quebec. 

It  is  used  chiefly  as  an  insulator  in  electrical  apparatus.  For  use  on 
commutators,  phlogopite  is  preferred  to  muscovite  as  it  has  more  nearly 
the  same  hardness  as  the  copper  of  the  commutator  segments. 

MUSCOVITE  (White  Mica,  Potash  Mica,  Isinglass),  H2KAl3(SiO4)3. 

Monoclinic,  prismatic  class.  Crystals  are  usually  tabular,  and 
possess  an  orthorhombic  or  hexagonal  outline  (Figs.  612  and  613). 


FIG.    611.  — Phlogopite. 
Lanark  County,  Ontario. 


FIG.  612. — Muscovite  (orthorombic  outline). 
Buckfield,  Maine. 


FIG.  613. — Muscovite  (hexagonal 
outline)  bordered  with  lepidolite.  Au- 
burn, Maine. 


Tapering  pyramidal  habits  are  also  observed.  Crystals  are  often  large 
and  rough,  measuring  at  times  several  feet  in  diameter.  Large  crystals 
may  show  distinct  partings  perpendicular  to  the  cleavage,  and  are  then 
called  ruled,  ribbon,  or  A  mica.  The  term  wedge  mica  is  applied  to  crystals 


296  MINERALOGY 

that  are  thicker  at  one  end  than  at  the  other.  Usually  occurs  in  scaly, 
foliated,  and  plumose  aggregates. 

Highly  perfect  basal  cleavage,  permitting  very  thin,  transparent, 
and  elastic  leaves  to  be  split,  Hardness  2  to  3.  Specific  gravity  2.8  to 
3.1.  Colorless,  yellowish,  brownish,  or  reddish.  Transparent  to  trans- 
lucent. Pearly  to  vitreous  luster. 

H2KAl3(SiO4)3.  Frequently  contains  small  amounts  of  calcium, 
magnesium,  iron,  sodium,  and  fluorine.  Fuchiste  contains  small  amounts 
of  chromium,  while  roscoelite  has  considerable  vana'dium  replacing  the 
aluminum.  Fuses  with  difficulty  to  a  grayish  or  yellowish  glass.  Not 
attacked  by  common  acids  Sericite  is  a  variety  consisting  of  fine  scaly 
aggregates  with  a  silky  luster.  It  often  results  from  the  alteration  of 
feldspars. 

Muscovite  is  generally  considered  the  most  common  mica.  It  occurs 
in  granites  and  syenites,  and  especially  in  pegmatite  veins  where  pneuma- 
tolytic  action  has  been  effective.  It  is  also  common  in  metamorphic 
rocks,  such  as  gneisses  and  schists,  and  in  some  limestones  and  fragmental 
rocks.  The  usual  associates  are  feldspar,  quartz,  tourmaline,  beryl, 
spodumene,  garnet,  apatite,  and  fluorite.  Deposits  of  muscovite  of 
commercial  value  occur  in  North  Carolina,  New  Hamsphire,  South 
Dakota,  Idaho,  New  Mexico,  Colorado,  Virginia,  South  Carolina,  Georgia, 
and  Alabama.  Some  of  the  principal  producing  localities  are  in  Mitchell, 
Yancey,  Macon,  Jackson,  Hay  wood,  and  Ashe  Counties,  North  Carolina; 
Custer  County,  South  Dakota;  Graf  ton  and  Cheshire  counties,  New 
Hampshire.  Deposits  of^excellent  rriuscovite  also  occur  in  Ottawa  and 
Berthier  counties,  Quebec. 

Sheet  mica  is  used  principally  in  the  manufacture  of  electrical  appara- 
tus and  machinery  such  as  dynamos,  motors,  high  voltage  induction 
apparatus,  switchboards,  lamp  sockets,  and  for  flexible  mica-covered 
insulating  cloth  and  tape.  Clear  and  transparent  sheets  are  used 
for  windows  in  coal,  gas,  and  oil  stoves,  gas-lamp  chimneys,  and  lamp 
shades.  Scrap  mica,  that  is,  material  too  small  to  be  cut  into  sheets, 
is  ground  in  large  quantities  and  used  in  the  manufacture  of  wall  paper, 
lubricants,  fancy  paints,  rubber  goods,  electrical  insulators,  coverings 
for  steam  pipes,  and  roofing  papers. 

Micanite  is  prepared  by  cementing  with  shellac  successive  layers 
of  small,  thin  sheets  of  mica  and  subjecting  the  mass  to  heat  and 
pressure. 

United  States  consumes  about  75  per  cent,  of  the  world's  production 
of  mica;  80  to  90  per  cent,  is  of  domestic  origin,  the  remainder  being  im- 
ported from  Canada  and  India.  The  total  value  of  the  domestic  mica 
production  in  United  States  in  1918  was  $731,810,  representing  the  value 
of  1,644,200  Ibs.  of  sheet  mica  and  2,292  short  tons  of  scrap  mica. 


DESCRIPTIVE  MINERALOGY  297 

Lepidolite  (Lithium  Mica) ,  (Li,K)2(F,OH)2Al2Si3O9. 

•  Monoclinic,  prismatic  class.  Crystals  are  short  prismatic,  but  very 
rare.  Usually  in  scaly,  granular  masses,  often  resembling  granular 
limestone,  and  in  tabular,  cleavable  plates. 

Perfect  basal  cleavage.  Hardness  2  to  4.  Specific  gravity  2.8  to 
2.9.  Rose-red  or  lilac  in  color,  also  white,  gray,  greenish,  or  brown. 
Pearly  luster.  Translucent. 

(Li,K)2(F,OH)2Al2Si3O9.  Some  varieties  contain  rubidium  and 
caesium.  Colors  the  flame  red  and  fuses  to  a  white  glass.  After  fusion 
easily  acted  upon  by  acids. 

Occurs  commonly  in  pegmatite  veins,  also  in  granites  and  gneisses. 
It  is  usually  the  result  of  pneumatolytic  action.  The  common  associates 
are  tourmaline  (especially  rubellite),  (Fig.  596,  page  286),  spodumene, 
cassiterite,  muscovite,  albite,  and  topaz.  Some  localities  are:  Rozena, 
Moravia;  Island  of  Elba;  Paris,  Hebron,  Auburn,  and  Rumford,  Maine; 
Chesterfield,  Massachusetts;  San  Diego  County,  California. 

An  important  source  of  lithium  compounds. 


CHLORITE,  Prochlorite,  Ctinochlorite,  H8Mg5Al2Si3Oi8. 

The  general  term  chlorite  is  applied  to  a  number  of  minerals  which  are 
closely  related  to  the  micas. 

Monoclinic,  prismatic  class.  Crystals  are  tabular  and  six-sided, 
resembling  those  of  mica.  Commonly  in  foliated,  scaly,  granular,  or 
earthy  masses.  Often  as  a  scaly  or  dusty  coating  on,  or  disseminated 
through,  quartz,  titanite,  pericline,  and  adularia. 

Perfect  basal  cleavage.  Laminae  are  flexible  but  inelastic.  Slightly 
soapy  feel.  Hardness  1  to  2.5.  Specific  gravity  2.6  to  3.  Grass  green, 
brownish  green,  or  blackish  green  in  color.  Translucent  to  opaque, 
very  thin  laminse  may  be  transparent.  Streak,  greenish. 

The  minerals  included  in  this  description  are  silicates  of  aluminum  or 
trivalent  iron  with  magnesium,  bivalent  iron,  or  manganese.  They  are 
more  basic  than  the  micas,  and  are  free  from  the  alkalies  and  calcium. 
The  composition  varies  greatly.  They  yield  water  when  heated  in  a 
closed  tube. 

These  minerals  are  of  secondary  origin,  and  are  usually  the  result  of 
the  decomposition  of  pyroxenes,  amphiboles,  garnet,  biotite,  and  vesuv- 
ianite.  Very  common  in  schists  and  serpentine.  Often  associated  with 
garnet,  diopside,  magnesite,  magnetite,  and  apatite.  Very  widespread. 
Some  principal  localities  are:  Ural  Mountains;  various  places  in  Tyrol; 
Zermatt,  Switzerland;  Saxony;  Chester  and  Union ville,  Pennsylvania; 
Brewster,  New  York . 

SERPENTINE,  H4Mg3Si2O9. 

Monoclinic,  optically.  Never  in  crystals  except  pseudomorphs. 
Usually  compact,  columnar,  fibrous,  or  lamellar.  Massive  varieties 
often  have  a  microscopically  fine  fibrous  or  foliated  structure. 


298 


MINERALOGY 


Conchoidal  to  splintery  fracture.  Hardness  2.5  to  4.  Specific 
gravity  2.5  to  2.8.  Various  shades  of  green,  also  yellowish,  grayish, 
reddish,  brownish,  or  black.  Often  spotted,  clouded,  or  multi-colored. 
Dull  resinous,  greasy,  or  waxy  luster.  Smooth  to  greasy  feel. 


FIG.  614. — Serpen- 
tine: Variety,  asbestos. 
Near  Globe,  Arizona. 


FIG.  615. — Serpentine:  Variety,  as- 
bestos (light).*  Thetford  Lake  District, 
Canada. 


n 


There  are  several  varieties: 

(1)  Common    Serpentine. — Compact,    massive.     Generally    dark 
color,  often  multi-colored.     Sometimes  impure.     Very  abundant. 

(2)  Precious   Serpentine. — Massive,    more 
or    less    homogeneous.      Various    shades    of 
green  in  color,  sometimes  yellowish.     Trans- 
lucent. 

(3)  Chrysotile,  Fibrous  Serpentine,  Asbes- 
tos.— Consist  of  delicate,  fine,  parallel  fibers, 
which   can   be   easily   separated    (Fig.  614). 
Fibers  are  flexible  and  adapted  for  spinning. 
Silky  to  silky  metallic  luster.     Various  shades 
of    green    in  color,  also  white,  yellowish  or 
brownish      Usually  found  in  veins  with  the 
fibers  perpendicular  to  the  walls  of  the  veins 
(Fig.    615).     Sometimes    called    short  fibered 
asbestos. 

(4)  Verd-antique. — Massive   greenish   ser- 
pentine mixed  irregularly  with  calcite,  dolo- 
mite, or  magnesite,  having  a  mottled  or  veined  appearance  (Fig.  616). 
Takes  an  excellent  polish  and  is  used  extensively  for  ornamental  pur- 
poses.    It  is  sometimes  called  serpentine  marble. 

H4Mg3Si209.     May   contain   iron   and   nickel.     Yields   water   when 
ignited.     Splinters  fuse  with  difficulty.     Decomposed  by  acids  with  a 


FIG.  616.— Serpentine:  Va- 
riety, verd-antique.  Roxbury, 
Vermont. 


DESCRIPTIVE  MINERALOGY  299 

separation  of  silica.  May  alter  to  brucite,  magnesite,  and  hydromagne- 
site.  Serpentine  is  a  secondary  mineral  resulting  from  the  alteration  of 
magnesium  minerals  and  rocks,  such  as  olivine,  enstatite,  hornblende, 
tremolite,  augite,  chondrodite,  and  peridotite.  Olivine  is  the  most 
common  source  of  serpentine.  Common  associates  are  magnesite,  cal- 
cite,  chromite,  garnierite,  pyrope,  platinum,  and  talc. 

Serpentine  occurs  in  many  localities,  some  of  which  are:  Sweden; 
Silesia;  Chester  County  and  Easton,  Pennsylvania,  where  it  is  mined; 
Milford,  Connecticut;  Hoboken  and  Montville,  New  Jersey;  Syracuse, 
New  York;  Vermont;  northern  New  York;  Washington.  Asbestos  is  not 
found  to  any  extent  in  the  United  States.  Most  of  the  asbestos  of  com- 
merce is  obtained  from  the  mines  in  the  Thetford-Black  Lake  district, 
Quebec.  In  1918,  the  imports  of  asbestos,  almost  wholly  from  Canada, 
amounted  to  137,700  short  tons. 

Polished  massive  serpentine  and  verd-antique  are  used  for  ornamental 
and  interior  decorative  purposes.  Translucent  yellowish  serpentine  is 
sometimes  cut  and  polished  for  gem  purposes.  Asbestos  is  used  exten- 
sively in  the  manufacture  of  non-conductors  of  heat  and  in  non-combustible 
materials  such  as  cloth,  boards,  felt,  rope,  paper,  paint,  cement,  and 
theater  curtains. 

TALC,  H2Mg3Si4012. 

Monoclinic.  Crystals  are  tabular  or  scaly,  but  indistinctly  developed. 
Occurs  usually  as  foliated  or  compact  masses,  and  globular  or  stellate 
groups;  also  fibrous  or  granular. 

Perfect  basal  cleavage.  Laminae  are  flexible  but  inelastic.  Compact 
varieties  have  an  uneven  fracture.  Hardness  1  to  2.5.  Specific  gravity 
2.6  to  2.8.  Commonly  green,  white,  or  gray  in  color;  also  yellowish, 
reddish,  and  brown.  Greasy  or  soapy  feel.  Opaque  to  transparent. 

There  are  several  varieties  of  talc: 

(1)  Foliated  Talc. — Consists  of  easily  separable  but  inelastic  scales 
or  plates.     Soapy  or  greasy  feel.     Hardness  1,  easily  impressed  by  the 
finger  nail.     Light  green  to  white  in  color. 

(2)  Steatite  or  Soapstone. — Massive,  often  impure.     Coarse  to  fine 
granular,  also  schistose.     Gray   to  greenish  in  color.     Hardness  1.5  to 
2.5.     Occurs  in  large  deposits. 

(3)  French   Chalk. — Soft,    compact,    whitish   masses.     Marks   cloth 
easily. 

H2Mg3Si4Oi2.  May  contain  iron,  aluminum,  and  nickel.  Fuses 
with  great  difficulty.  Yields  water  when  strongly  ignited.  Unattacked 
by  acids.  Occurs  as  a  pseudomorph  after  pyroxene,  hornblende,  tre- 
molite, enstatite,  spinel,  quartz,  dolomite,  and  many  other  minerals. 

Talc  is  usually  considered  an  alteration  product  of  non-aluminous 
magnesium  minerals,  such  as  the  pyroxenes,  amphiboles,  and  olivine. 
Commonly  found  in  metamorphic  rocks,  especially  chlorite  schists;  also 


300  MINERALOGY 

with  serpentine  and  dolomite.  Occurs  frequently  as  talc  •  or  talcose 
schist  containing  doubly  terminated  crystals  of  magnetite,  dolomite, 
apatite,  tourmaline,  pyrite,  and  actinolite.  Foliated  talc  is  found  at 
Greiner,  Tyrol;  various  places  in  Switzerland,  Italy,  France,  and  Ger- 
many; Graf  ton  and  elsewhere,  New  Hampshire;  St.  Lawrence  County, 
New  York.  The  most  important  producing  locality  in  the  United  States 
for  talc  and  soapstone  is  in  St.  Lawrence  County,  New  York,  where 
talc  occurs  with  limestone,  and  has  been  derived  from  tremolite  and  en- 
statite.  Vermont  is  also  an  important  producer  of -talc.  Albermarle 
and  Nelson  counties,  Virginia,  Montgomery  and  Northhampton  counties, 
Pennsylvania,  and  Phillipsburg,  New  Jersey  also  produce  large  quantities. 
Other  important  localities  are  in  North  Corolina,  Georgia,  Maryland, 
Rhode  Island,  Massachusetts,  and  California. 

Talc  and  soapstone,  cut  into  slabs  or  other  shapes,  are  used  for 
washtubs,  sanitary  appliances,  laboratory  tables  and  tanks,  electrical 
switch  boards,  mantels,  hearthstones,  fire-bricks,  foot  warmers,  slate 
pencils,  and  as  crayon  for  marking  iron,  glass,  and  fabrics.  Ground  talc 
is  used  in  toilet  powders  and  soaps,  for  dressing  skins  and  leather,  as  a 
lubricant,  non-conductor  of  heat,  and  as  ''mineral  pulp"  as  a  filler  in 
paint  and  paper. 

Sepiolite  (Meerschaum),  H4Mg2Si3Oio. 

Monoclinic.  Occurs  only  in  compact  nodular,  earthy,  or  clayey 
masses. 

Conchoidal  to  uneven  fracture.  Hardness  2  to  2.5.  Impressed  by 
the  finger  nail.  Specific  gravity  1  to  2.  On  account  of  its  porosity  it 
may  float  on  water.  Adheres  to  the  tongue.  Usually  white,  yellowish, 
or  grayish  in  color.  Dull  luster. 

H4Mg2Si3Oio.  Yields  water  when  strongly  ignited.  Fuses  with 
difficulty  on  thin  edges  to  a  white  glass;  some  varieties  first  turn  black. 
Gelatinizes  with  hydrochloric  acid. 

An  alteration  product  of  serpentine,  magnesite,  or  impure  opal  con- 
taining considerable  magnesium.  It  is  found  principally  in  nodular 
masses  in  serpentine  or  in  secondary  deposits,  on  the  plains  of  Eskishehr, 
Asia  Minor.  Occurs  in  smaller  quantities  in  Spain;  the  Grecian  Archi- 
pelago; Morocco;  Moravia;  Utah;  California;  New  Mexico. 

Meerschaum  is  easily  carved  and  worked  on  the  lathe,  takes  an  ex- 
cellent polish,  and  is  used  extensively  for  pipe  bowls  and  cigar  tips. 
Claimed  to  be  a  building  stone  in  Spain. 

Garnierite,  H2(Ni,Mg)SiO4. 

Never  found  in  crystals.  Occurs  commonly  as  rounded,  pea- 
shaped  masses  with  varnish-like  surfaces;  also  compact,  reniform  or 
earthy;  apparently  amorphous. 

Conchoidal  or  earthy  fracture.     Hardness  2  to  3.     Specific  gravity 


DESCRIPTIVE  MINERALCtGY  301 

2.3  to  2.8.  Pale,  apple,  or  emerald  green  in  color.  Dull  to  greasy 
luster.  Greasy  feel.  Frequently  adheres  to  the  tongue.  Streak, 
white  to  greenish. 

H2(Ni,Mg)SiO4.  Composition  varies  greatly.  Infusible,  decrepi- 
tates, and  becomes  magnetic.  Yields  water  on  ignition.  Attacked  by 
acids. 

An  alteration  of  olivine  and  serpentine  rocks.  Usually  associated 
with  olivine,  serpentine,  chromite,  and  talc.  Occurs  in  serpentine  at 
Noumea,  New  Caledonia;  also  found  at  Franckenstein,  Silesia;  Webster, 
North  Carolina;  Riddles,  Douglas  County,  Oregon. 

A  valuable  source  of  nickel. 


KAOLINITE  (Kaolin,  China  Clay), 

Monoclinic,  prismatic  class.  Rarely  in  small  scales  with  an  hex- 
agonal or  orthorhombic  outline.  Generally  in  compact,  friable,  mealy, 
or  clay-like  masses. 

Scales  possess  a  basal  cleavage.  Earthy  fracture.  Hardness  1  to 
2.5.  Specific  gravity  2.2  to  2.6.  Compact  masses  are  dull,  scales  pearly. 
White,  yellowish,  reddish,  bluish,  greenish,  or  brownish  in  color.  Greasy 
feel.  White  to  yellowish  streak.  Opaque  to  translucent.  Usually 
adheres  to  the  tongue  and  becomes  plastic  when  moistened.  Argilla- 
ceous odor  when  breathed  upon. 

H4Al2Si2O9.  May  contain  some  iron.  Yields  water  on  ignition. 
Infusible.  Partially  decomposed  by  hydrochloric  acid.  Occurs  as  a 
pseudomorph  after  many  minerals. 

Kaolinite  is  always  a  secondary  mineral  resulting  from  the  action  -of 
post-volcanic,  pneumatolytic,  and  hydrothermal  processes  upon  rocks 
containing  feldspar,  nephelite,  topaz,  beryl,  augite,  scapolite,  and  other 
aluminous  minerals.  It  may  also  result  from  ordinary  weathering.  Oc- 
curs in  irregular  deposits  in  kaolinized  granites,  porphyries,  and  gneisses. 
Also  in  secondary  deposits,  the  result  of  transportation  and  deposition 
under  water.  These  occurrences  are  often  very  pure.  It  is  an  impor- 
tant constituent  of  clay  and  soil.  Common  associates  are  feldspar, 
quartz,  corundum,  and  diaspore.  Some  localities  are:  St.  Yrieix,  near 
Limoges,  France;  Cornwall  and  Devonshire,  England;  Meissen,  Saxony. 
In  the  United  States  kaolin  is  mined  at  Newcastle  and  Wilmington, 
Delaware;  also  in  Florida,  North  Carolina,  Pennsylvania,  Vermont, 
California,  and  Maryland. 

Kaolinite  is  used  in  large  quantities  in  the  manufacture  of  china- 
ware,  porcelain,  tiles,  and  other  refractory  materials. 

NEPHELITE  (Nepheline),  (Na,K)8Al8Si9O34. 

Hexagonal,  pyramidal  class.  Crystals  are  short  prismatic  or  tabular. 
Commonly  in  compact  masses  or  as  disseminated  grains. 

Imperfect   prismatic   and   basal   cleavages.     Conchoidal   to   uneven 


302  MINERALOGY 

fracture.  Hardness  5  to  6.  Specific  gravity  2.55  to  2.65.  Colorless, 
white,  yellowish,  greenish,  gray,  or  reddish.  Greasy  luster  on  cleavages, 
otherwise  vitreous.  Transparent  to  opaque. 

There  are  two  varieties: 

Nephelite  Proper. — This  includes  the  light  colored,  glassy  occurrences 
showing  in  many  instances  a  definite  crystal  outline.  Common  in  the 
more  recent  eruptive  rocks.  Transparent  to  translucent. 

Elaeolite. — This  is  a  massive  or  granular  variety  and  rarely  shows  a 
definite  outline.  Gray  or  more  highly  colored — green,  red,  brown,  or 
blue.  Cloudy  or  opaque.  Greasy  luster.  Common  in  the  older  plutonic 
rocks,  such  as  syenites,  phonolites,  and  basalts. 

(Na,K)8Al8Si9034.  Composition  varies  greatly.  Formula  is  some- 
times given  as  NaAlSiO4,  the  composition  of  synthetic  soda-nephelite. 
Potassium  is  usually  present,  also  small  amounts  of  calcium,  lithium,  and 
chlorine.  Fuses  easily  to  a  colorless  glass.  Gelatinizes  with  hydro- 
chloric acid,  yielding  on  evaporation  cubes  of  NaCl.  Alters  readily  to 
hydronephelite,  sodalite,  muscovite,  cancrinite,  analcite,  kaolinite,  or 
garnet.  Pseudomorphous  after  leucite. 

Nephelite  is  commonly  associated  with  feldspar,  cancrinite,  biotite, 
sodalite,  corundum,  and  zircon;  but  not  with  primary  quartz.  Some 
localities  are:  Mount  Vesuvius;  Katzenbuckel,  Baden;  Laacher  See, 
Rhenish  Prussia;  Southern  Norway;  Ural  Mountains;  Brazil;  Ontario, 
Canada;  Litchfield,  Maine;  Cripple  Creek,  Colorado;  Magnet  Cove, 
Arkansas;  Salem,  Massachusetts. 

Nephelite  is  of  no  importance  commercially.     . 

Cancrinite,  H6(Na2,Ca)4(NaCO3)2Al8Si9O36. 

Hexagonal,  dihexagonal  bipyramidal  class.  Crystals  are  columnar 
or  prismatic,  but  rare.  Usually  in  compact,  lamellar,  columnar,  or 
disseminated  masses. 

Perfect  prismatic  cleavage.  Uneven  fracture.  Hardness  5  to  6. 
Specific  gravity  2.45.  Generally  colored — lemon  to  brownish  yellow, 
reddish,  green;  sometimes  gray,  white,  or  colorless.  Pearly  luster  on 
cleavages,  elsewhere  vitreous  to  greasy.  Transparent  to  translucent. 
Fuses  easily  with  intumescence  to  a  white  blebby  glass.  Upon  ignition 
turns  white  and  yields  water.  Effervesces  with  hydrochloric  acid  and 
gelatinizes  on  heating. 

Commonly  associated  with  sodalite,  nephelite,  biotite,  feldspar,  tita- 
nite,  and  apatite.  May  be  a  primary  constituent  of  igneous  rocks,  al- 
though in  most  cases  it  is  secondary,  resulting  from  the  alteration  of 
nephelite.  Occurs  in  nephelite  syenites  at  Barkevik,  Norway;  Miask, 
Ural  Mountains;  Finland;  Sweden;  Hungary;  province  of  Quebec, 
Canada;  Litchfield,  Maine. 

Cancrinite  is  of  no  importance  commercially. 


DESCRIPTIVE  MINERALOGY 


303 


Sodalite,  Na4Al2(AlCl)  (SiO4) ,. 

Cubic,  hextetrahedral  class.  Crystals  are  not  common;  when 
observed  usually  rhombic  dodecahedrons.  Generally  in  compact, 
cleavage,  nodular,  or  disseminaed  masses. 

Distinct  dodecahedral  cleavage.  Uneven  to  conchoidal  fracture. 
Hardness  5  to  6.  Specific  gravity  2.2  to  2.4.  Vitreous  luster  on  crystal 
faces,  greasy  on  cleavages.  Usually  blue  in  color;  also  white,  green, 
reddish,  or  gray.  Transparent  to  opaque.  Colored  varieties  turn  white 
when  heated.  Fuses  with  intumescence  to  a  colorless  glass.  NaCl 
may  be  extracted  by  digesting  the  finely  powdered  mineral  with  water. 
Gelatinizes  with  hydrochloric  acid. 

Commonly  associated  with  nephelite,   cancrinite,  leucite,  feldspar, 
and  zircon;  but  not  with  quartz.     Occurs  at  Miask,  Ural  Mountains; 
Mount  Vesuvius;  Norway;  provinces  of  Quebec 
and      Ontario,      Canada;     Litchfield,     Maine; 
Montana. 

Sodalite  is  of  no  importance  commercially. 

Lazurite     (Lapis-Lazuli,    Native      Ultramarine) 

(Na2,Ca)2Al2[Al(NaS04,NaS3,Cl)](Si04)3. 

Cubic.  Crystals  are  rare,  either  dodecahe- 
dral or  cubic  in  habit.  Usually  as  irregular 
grains,  or  in  masses  containing  disseminated 
pyrite  (Fig.  617). 

Uneven  fracture.  Hardness  5  to  5.5.  Speci- 
fic gravity  2.4.  Vitreous  to  greasy  luster.  Deep 
to  azure  blue  in  color,  sometimes  violet  to  green- 
ish blue.  Opaque  to  translucent.  Fuses  easily 

to  a  white  blebby  glass.     Gelatinizes  with  hydrochloric  acid,  loses  color, 
and  evolves  an  odor  of  hydrogen  sulphide. 

Lazurite  is  a  contact  mineral  and  occurs  in  crystalline  limestones. 
The  principal  localities  are:  Afghanistan;  southern  end  of  Lake  Baikal, 
Siberia;  Ovalle,  Chile;  Cascade  Canyon,  San  Bernardino  County, California. 

Lazurite  is  highly  valued  for  ornaments,  mosaics,  and  vases.  It  was 
formerly  used  as  a  pigment  in  oil  painting. 

Ilmenite  (Menaccanite,  Titanic  Iron  Ore),  FeTiO3. 

Hexagonal,  trigonal  rhombohedral  class.  Crystals  are  tabular  or 
rhombohedral  in  habit  and  resemble  those  of  hematite.  Occasionally 
rhombohedrons  of  the  second  and  third  orders  are  present.  Generally 
in  compact  or  granular  masses,  also  in  thin  plates  or  disseminated  grains, 
or  as  pebbles  or  sand. 

No  cleavage,  but  basal  and  rhombohedral  partings.  Conchoidal  to 
uneven  fracture.  Hardness  5  to  6.  Specific  gravity  4.3  to  5.5.  Iron 
to  brownish  black  in  color.  Black  to  brownish  red  streak.  Metallic 


FIG.  617. — Lazurite  (lapis 
lazuli).     Persia. 


304  MINERALOGY 

to  submetallic  luster.  Opaque;  thin  plates  are  brown  in  transmitted 
light.  Slightly  magnetic,  greatly  increased  by  heating. 

FeTiO3.  Magnesium  or  manganese  may  replace  some  of  the  iron. 
Infusible.  Yields  a  blue  or  violet  solution  after  fusion  with  sodium 
carbonate  and  subsequent  boiling  with  hydrochloric  acid  and  tin  foil. 

As  an  accessory  mineral  it  is  common  in  many  igneous  and  meta- 
morphic  rocks,  such  as,  granite,  syenite,  diorite,  diabase,  gneiss,  and 
mica  schist.  Also  found  in  large  quantities  in  black  sands.  Common 
associates  are  hematite,  magnetite,  apatite,  serpentine,  titanite,  rutile, 
and  quartz.  Some  localities  are:  Kragero,  Snarum,  and  elsewhere, 
Norway;  various  places  in  Sweden;  St.  Gothard  district  and  Binnenthal, 
Switzerland;  province  of  Quebec,  Canada;  Orange  County,  New  York; 
Magnet  Cove,  Arkansas. 

It  is  used  in  the  preparation  of  linings  for  puddling  furnaces  and  in 
making  ferro-titanium.  On  account  of  the  difficulty  in  reducing  it, 
ilmenite  is  not  used  to  any  extent  as  an  ore  of  iron. 

Pyroxene  Group 

The  members  of  the  pyroxene  group  are  important  rock  minerals. 
They  consist  of  metasilicates  of  calcium,  magnesium,  iron,  aluminum, 
sodium,  lithium,  manganese,  and  zinc,  corresponding  to  the  general 
formula  M//2(SiO3)2.  Although  these  minerals  crystallize  in  three 
different  systems — orthorhombic,  monoclinic,  and  triclinic — they  are 
all  characterized  by  prism  angles  and  cleavages  of  about  87°  and  93°. 
The  orthorhombic  pyroxenes  generally  contain  no  calcium  and  little 
or  no  aluminum.  The  monoclinic  members  usually  have  considerable 
calcium  and  may,  or  may  not,  contain  aluminum  and  the  alkalies.  In 
the  triclinic  series  manganese  is  an  important  constituent. 

The  following  important  pyroxenes  will  be  described : 

Enstatite,  Bronzite,  Hypersthene    (Mg,Fe)2(SiO3)-.>  Orthorhombic 

Diopside                                                CaMg(SiO3)2  Monoclinic 

Wollastonite                                         Ca2(SiO3)2  Monoclinic 

~(Mg,Fe)Ca(SiO3)(SiO3) 


Augite 


(Mg,Fe)Al(A10,)(SiO,) 


Monoclinic 


(Mg,Fe)Fe(FeO3)(SiO3) 

Pectolite                                                (Ca,Na2)2(SiO3)2  Monoclinic 

Spodumene                                          LiAl(SiO3)2  Monoclinic 

Rhodonite                                             Mn2(SiO3)2  Triclinic 

The  pyroxenes  are  rather  closely  related,  chemically  and  crystal- 
lographically,  to  the  minerals  of  the  amphibole  group.  This  relationship 
will  be  discussed  on  page  310. 

ENSTATITE,  Bronzite,  Hypersthene  (Mg,Fe)2(SiO3)2. 

Orthorhombic,  bipyramidal  class.  Rarely  found  in  distinct  crystals, 
usually  in  fibrous,  lamellar,  columnar,  or  compact  masses.  Hypersthene 
occurs  frequently  in  cleavable  aggregates. 


DESCRIPTIVE  MINERALOGY 


305 


Prismatic  and  pinacoidal  cleavages.  Hardness  5  to  6.  Specific 
gravity  3.1  to  3.5.  Translucent  to  opaque. 

Enstatite. — Grayish  white,  greenish,  or  brownish  in  color.  Vitreous 
to  pearly  luster.  Contains  little  or  no  iron. 

Bronzite. — Darker  in  color  than  enstatite,  usually  brown,  yellowish, 
or  green.  Pronounced  pinacoidal  parting,  producing  fibrous  or  irregular 
wavy  surfaces  with  a  chatoyant  bronzy  luster.  Contains  from  5  to  16 
per  cent,  of  iron. 

Hypersthene. — Black,  brownish  black,  or  green  in  color.  Pearly  to 
metalloidal  luster.  Often  shows  a  copper  red  iridescence  on  the  macro- 
pinacoid.  Contains  more  iron  than  magnesium. 

These  minerals  occur  commonly  in  basic  igneous  rocks  such  as  pyrox- 
enite,  peridotite,  norite,  and  gabbro.  The  most  frequent  associates  are 


FIG.  618. 


FIG.    619. 


FIG.  620. — Diopside  with  zonal  distribution 
of  color.     Ala,  Italy. 


olivine,  chondrodite,  serpentine,  talc,  labradorite,  hornblende,  pyr- 
rhotite,  and  magnetite.  Some  localities  are:  Norway;  Austria;  Bavaria; 
Kimberley,  South  Africa;  St.  Paul's  Island,  off  the  coast  of  Labrador; 
Laacher  See,  Rhenish  Prussia;  Greenland;  Scotland;  along  the  Hudson 
River  and  in  the  Adirondack  Mountains,  New  York. 

Hypersthene  showing  an  iridescence  and  metalloidal  luster  is  some- 
times used  in  jewelry. 

DIOPSIDE,   CaMg(Si03)2. 

Monoclinic,  prismatic  class.  Crystals  are  generally  short  and  thick, 
and  nearly  square  or  octagonal  in  cross-section,  the  faces  of  the  unit 
prism  intersecting  at  angles  of  87°  and  93°.  Striations  parallel  to  the 
basal  pinacoid  are  frequently  observed  on  the  faces  of  the  vertical  zone. 
Common  forms  are  the  three  pinacoids,  unit  prism,  positive  and  negative 
hemi-pyramids,  and  the  positive  hemiorthodome  (Figs.  618,  619.  and 
620).  Occurs  also  in  compact,  broad  columnar,  granular,  lamellar, 
or  fibrous  masses. 
20 


306  MINERALOGY 

Prismatic  cleavage  and  basal  parting  are  conspicuous.  Hardness 
5  to  6.  Specific  gravity  3.2  to  3.3.  Uneven  to  conchoidal  fracture. 
Vitreous,  resinous,  or  dull  luster;  sometimes  inclining  to  pearly  on  the 
basal  parting.  Generally  light  to  dark  green  in  color;  also  colorless,  gray, 
yellow,  and  rarely  blue.  Zonal  distribution  of  color  not  uncommon 
(Fig.  620).  White  to  greenish  streak.  Transparent  to  opaque. 

CaMg(SiO3)2.  Usually  contains  up  to  5  per  cent,  of  FeO.  Diallage 
is  a  thin  foliated,  or  lamellar  variety,  containing  from  8  to  16  per  cent,  of 
iron  oxide,  and  greenish  or  brownish  in  color.  Aluminum  and  man- 
ganese may  also  be  present.  More  or  less  fusible  to  a  dark  colored  or 
green  glass.  Not  acted  upon  by  the  common  acids.  Alters  to  serpen- 
tine, talc,  chlorite,  and  limonite. 

Occurs  in  granite,  gabbro,  basalt,  pyroxenite,  and  peridotite;  also  in 
crystalline  schists  and  as  a  contact  mineral  in  limestone  and  dolomite. 

Common  associates  are  vesuvianite,  tre- 
molite,  garnet,  scapolite,  spinel,  apatite, 
titanite,  phlogopite,  amphibole,  tourmaline, 
and  the  feldspars.  Found  at  various  places 
in  Tyrol;  Zermatt,  Switzerland;  Pargas, 
Finland;  Sweden;  Lanark  and  Hastings 
counties,  Ontario;  Lewis  and  St.  Lawrence 
counties,  New  York. 

Clear    and    transparent    varieties    are 
sometimes  used  for  gem  purposes. 

Wollastonite  (Tabular  Spar),  Ca2(SiO3)2. 

Monoclinic,    prismatic    class.     Crystals 
are  usually  elongated  parallel  to  the  b  axis 
FIG  621.— Wollastonite     an(j    tabular    in   habit.     Most    commonly 

Bucks  County,  Pennsylvania.  .         .  .      /  .      £ 

observed  in  cleavable  (Fig.  621),  fibrous, 

granular,  and  compact  masses.  The  fibers  may  have  a  parallel  or  di- 
vergent structure. 

Basal  and  orthopinacoidal  cleavages.  Uneven  fracture.  Hardness 
4  to  5.  Specific  gravity  2.8  to  2.9.  Usually  white,  colorless,  or  gray; 
also  yellowish,  reddish,  or  brownish.  Vitreous  to  silky  luster.  Trans- 
parent to  translucent. 

Ca2(SiO3)2.  Generally  mixed  with  calcite,  and  hence  effervesces 
with  acid.  Fusible  on  the  thin  edges.  Decomposes  with  hydrochloric 
acid  with  separation  of  silica. 

Wollastonite  is  a  typical  contact  metamorphic  mineral  and  is  gener- 
ally associated  with  garnet,  diopside,  vesuvianite,  tremolite,  graphite, 
epidote,  and  calcite.  It  is  found  in  granular  limestone,  granite,  and  basalt. 
Some  localities  are:  the  Island  of  Elba;  Norway;  Mount  Vesuvius;  Hun- 
gary; Grenville,  Quebec;  North  Burgess  and  elsewhere,  Ontario;  Lewis 
and  Warren  counties,  New  York;  California. 


DESCRIPTIVE  MINERALOGY 


307 


AUGITE. 

Monoclinic,  prismatic  class.  Crystal  are  short,  prismatic,  or  thick 
columnar  with  a  prism  angle  of  87°,  yielding  a  pseudotetragonal  outline. 
The  most  usual  combination  consists  of  the  ortho-  (a)  and  clinopinacoids 
(6),  unit  prism  (m),  positive  unit  hemi-pyramid  (o)  and  negative  hemi- 
orthodome  (t)  (Figs.  622  and  623) .  Sometimes  occurs  as  contact  twins, 
twinned  parallel  to  the  orthopinacoid  (Fig.  624)  or  as  penetration  twins 


FIG.  622. 


FIG.  623. 


FIG.  624. 


FIG.  625. 


in  which  the  clinohemipyramid  is  the  twinning  plane  (Fig.  625).  It 
is  also  observed  in  compact  and  disseminated  grains  and  granular  ag- 
gregates; rarely  fibrous. 

Prismatic  cleavage.  Conchoidal  to  uneven  fracture.  Hardness 
5  to  6.  Specific  gravity  3.2  to  3.6,  varying  with  the  composition.  Com- 
monly black  or  greenish  black  in  color,  also  leek  green.  Grayish  green 
streak.  Usually  opaque,  but  may  be  translucent.  Vitreous  to  dull. 

Chemically,  augite  is  considered  an  isomorphous  mixture  of  (Mg,Fe)- 
Ca(Si03)(Si03),  (Mg,Fe)Al(A103)(Si03),  and  (Mg,Fe)Fe(FeO3)(SiO3). 
Sodium  and  titanium  are  sometimes  present.  Fuses  and  often  forms  a 
magnetic  glass.  Slightly  acted  upon  by  acids.  Alters  to  a  fibrous 
hornblende  having  the  form  of  augite,  termed  uralite,  and  also  to 
serpentine. 

Augite  is  a  common  rock  mineral,  and  often  occurs  in  disseminated 
crystals  as  an  essential  or  accessory  constituent  of  basalt,  melaphyre, 
diabase,  gabbro,  tuff,  and  volcanic  sand  and  ashes.  Also  occurs  in 
crystalline  schists  and  limestones,  and  is  commonly  the  result  of  contact 
metamorphism.  Some  notable  localities  are:  Fassathal,  Tyrol;  Mount 
Vesuvius;  Mount  Aetna;  Kaiserstuhl,  Baden;  Bohemia;  Norway;  Fin- 
land; Thetford,  Vermont;  Amherst  County,  Virginia. 
Pectolite  (Ca,Na2)2(SiO3)2. 

Monoclinic,  prismatic  class.  Crystals  are  commonly  tabular, 
but  rare.  Generally  consists  of  aggregates  of  divergent  fibers  or  acicular 
crystals,  sometimes  of  considerable  length  and  with  sharp  ends  (Fig. 
626). 


308 


MINERALOGY 


FIG.  626.— Pectolite.     Paterson, 
New  Jersey. 


Basal  and  orthopinacoidal  cleavages.  Uneven  fracture.  Hardness 
4  to  5.  Specific  gravity  2.7  to  2.8.  Colorless,  white,  or  grayish  white. 

Translucent  to  opaque.     Vitreous  pearly 
to  silky  luster. 

(Ca,Na2)2(SiO3)2.  Usually  contains 
about  10  per  cent,  of  sodium  oxide. 
Manganese  is  sometimes  present.  Yields 
water  in  a  closed  tube.  Decomposed  by 
hydrochloric  acid  with  the  separation  of 
silica.  Sometimes  phosphoresces  when 
crushed  in  the  dark. 

Occurs  in  fissures  and  cavities  in  basic 
igneous  and  metamorphic  rocks.  Com- 
monly associated  with  the  zeolites,  dato- 
lite,  and  calcite.  Some  localities  are:  Fassathal  and  Monzoni,  Tyrol, 
Scotland;  Thunder  Bay,  Ontario;  Bergen  Hill,  Paterson,  and  vicinity, 
New  Jersey;  Isle  Royale,  Michigan. 

SPODUMENE,  Hiddenite,  Kunzite,  LiAl(SiO3)2. 

Monoclinic,  prismatic  class.  Long,  columnar  crystals  with  the  unit 
prism  predominating;  also  tabular,  and  frequently  with  vertical  striations 
and  furrows  (Fig.  627).  Often  very  large,  several 
crystals  from  the  Etta  mine,  near  Keystone,  South 
Dakota,  having  measured  over  30  feet  in  length  and 
from  2J/2  to  6  feet  in  width.  Occurs  more  com- 
monly in  cleavable  masses  and  broad  columnar  ag- 
gregates. 

Perfect  prismatic  cleavage;  also  very  easy  part- 
ing parallel  to  the  orthopinacoid.  Uneven  to  splin- 
tery fracture.  Hardness  6  to  7.  Specific  gravity 
3.1  to  3.2.  White,  grayish,  green,  pink,  and  purple. 
Vitreous  to  pearly  luster.  Transparent  to  opaque. 
Hiddenite  is  a  clear  yellow  to  emerald  green  variety  FlG>  627.— Sppdu- 

f  ou  T-»    •     ,       A  i  i        ^  -x-r-i^.  mene.    Norwich,  Mas- 

trom  btony  Point,  Alexander  County,  North  Caro-    sachusetts. 
lina.     A  transparent  lilac  pink  variety  from  Pala, 
San  Diego  County,  California,  is  called  kunzite.     This  variety  phosphor- 
esces with  an  orange  pink  light  when  exposed  to  electric  discharges,  the 
X-rays,  ultra-violet  light,  or  to' radium  emanations. 

LiAl(SiO3)2.  Usually  contains  some  sodium,  iron,  and  calcium. 
Fuses  easily,  turns  white,  intumesces,  and  colors  the  flame  purple  red. 
Insoluble  in  acids.  Alters  to  albite,  muscovite,  and  quartz. 

Occurs  in  pegmatite  veins  with  tourmaline,  beryl,  garnet,  lepidolite, 
feldspar,  mica,  and  quartz  as  the  principal  associates.  Some  localities 
are:  Sweden;  Tyrol;  Ireland;  Windham,  Maine;  Sterling,  Chester,  and 
Goshen,  Massachusetts;  Branchville,  Connecticut;  Stony  Point, 


DESCRIPTIVE  MINERALOGY 


309 


Alexander  County,  North  Carolina;   Etta  mine,   Pennington  County, 
South  Dakota;  Pala,  San  Diego  County,  California. 

Hiddenite  and  kunzite  are  used  for  gem  purposes.  The  output  of 
the  Etta  mine,  near  Keystone,  South  Dakota,  furnishes  an  important 
source  of  lithium  compounds,  some  of  which  are  used  in  the  manufac- 
ture of  red  fire  and  for  medicinal  purposes. 

RHODONITE,  Fowlerite,   Mn2(SiO3)2. 

Triclinic,  pinacoidal  class.  Crystals  are  usually  tabular  or  prismatic, 
comparatively  large  and  with  rounded  edges,  but  not  very  common 
(Fig.  628).  Occurs  generally  in  fine  grained,  cleavable,  or  compact 
masses;  also  in  disseminated  grains. 

Prismatic  and  basal  cleavages.  Conchoidal  to  uneven  fracture. 
Hardness  5  to  6.  Specific  gravity  3.4  to  3.7.  Rose-red,  pink,  yellowish, 
greenish,  or  brownish  in  color;  often  black  exter- 
nally. Vitreous  to  pearly  luster.  Transparent  to 
opaque. 

Mn2(SiO3)2.  Commonly  contains  some  cal- 
cium and  iron.  Fowlerite  is  a  zinciferous  variety 
from  the  Franklin  Furnace  district,  New  Jersey. 
Fuses  easily  to  a  brownish  or  black  glass. 
Slightly  acted  upon  by  acids,  although  varieties 
containing  an  admixture  of  calcite  will  effervesce. 

Occurs  with  calcite,  rhodochrosite,  tetrahe- 
drite,  franklinite,  willemite,  zincite,  quartz,  and 
iron  ores.  Some  localities  are:  the  Hartz  Moun- 
tains; Hungary;  Italy;  Sweden;  Ural  Mountains; 
Peru;  Cummington,  Massachusetts;  Franklin  Franklin  Furnace,  New 
Furnace,  New  Jersey;  Butte,  Montana. 

Sometimes  used  for  gem  and  ornamental  purposes. 

Amphibole  Group 

The  members  of  the  amphibole  group  are  closely  related  to  the 
pyroxenes,  being  important  rock  minerals  and  metasilicates  of  magnesium, 
aluminum,  iron,  calcium,  sodium,  and  potassium  which  possess  the 
general  formula  M//4(Si03)4.  Like  the  pyroxenes,  these  minerals  also 
crystallize  in  the  orthorhombic,  monoclinic,  and  triclinic  systems,  but 
only  the  following  monoclinic  amphiboles  are  sufficiently  important  to 
warrant  description: 

Tremolite CaMg3(Si03)4 

Actinolite Ca(Mg,Fe)3(SiO3)4 

Ca(Mg,Fe)3(Si03)2(Si03)2 


FIG.  628. — Rhodonite. 


Hornblende 


Al2(Mg,Fe)3(A103)2(Si03)2 
Fe2(Mg,Fe)3(Fe03)2(Si03)2 


310 


MINERALOGY 


The  principal  differences  between  the  members  of  the  pyroxene  and 
amphibole  groups  may  be  tabulated  as  follows: 


Crystals 


Prism  angles 
Cleavages 

Masses 

Specific  gravity 
Chemical  composition 

Occurrence 


Pyroxenes 

Short,  prismatic,  complex, 
commonly  four-  or  eight- 
sided. 

87°  and  93° 

Prismatic,  nearly  90° 
bladed. 

Lamellar  or  granular 

Higher 

Alter  to  amphibole 

Common  in  more  basic 
rocks. 


Amphiboles 

Long     prismatic,     simple 
commonlv  six-sided. 


56°  and  124° 
Prismatic,      nearly 

more  distinct. 
Columnar  or  fibrous 


120C 


Magnesium  and  the  alka- 
lies are  more  prominent. 

Common  in  more  acid 
rocks. 


Tremolite,    CaMg3(SiO3)4. 

Monoclinic,   prismatic   class.     Crystals  are  bladed,   either  long  or 
short,  but  generally  without  terminal  faces   (Fig.   629).     Occurs  also 


FIG.  629. — Tremolite.     Haliburton,  Ontario. 


in  fibrous  and  asbestiform  aggregates,  and  in  compact  columnar  or 
granular  masses. 

Perfect  prismatic  cleavage,  at  angles  of  56°  and  124°.  Hardness  5  to  6. 
Specific  gravity  2.9  to  3.1.  Generally  white,  gray,  greenish,  or  yellowish 
in  color.  Hexagonite  is  an  amethystine  to  lavender  variety,  due  to  a  small 
amount  of  manganese.  Vitreous  to  silky  luster.  Transparent  to  opaque. 

CaMg3(SiO3)4.  Contains  little  or  no  iron.  Not  acted  upon  by 
acids.  Fuses  with  difficulty.  Alters  to  talc. 

Tremolite  is  a  contact  metamorphic  mineral,  and  occurs  in  granular 
limestones  and  dolomites,  and  schists.  Found  in  the  St.  Gotthard  district, 
Switzerland;  various  places  in  Sweden  and  Hungary;  Lee,  Massachusetts; 
Easton,  Pennsylvania;  Edenville,  Orange  County,  and  Edwards,  St. 
Lawrence  County,  New  York;  Pontiac  County,  Quebec;  Renfrew  and 
Lanark  counties,  Ontario. 


DESCRIPTIVE  MINERALOGY 


311 


Asbestos 

Under  this  term  are  included  fibrous  varieties  of  tremolite,  actinolite, 
and  other  non-aluminous  amphiboles.  The  fibers  are  sometimes  long, 
parallel,  flexible,  and  easily  separated  by  the  fingers.  Amphibole 
asbestos  is  commonly  called  long  fibered  asbestos,  while  serpentine  asbestos, 
see  page  298,  is  termed  short  fibered.  The  heat  resisting  property  of  the 
amphibole  asbestos  is  about  the  same  as  that  of  the  chrysotile  asbestos, 
but  the  non-conductivity  of  heat  and  strength  of  fiber  are  less.  It 
is  also  not  as  suitable  for  spinning  as  the  short  fibered  asbestos.  Hence, 
serpentine  or  chrysotile  asbestos  gives  the  better  results.  Amphibole 
asbestos  occurs  at  Sail  Mountain,  Georgia,  and  in  Lewis  County,  Idaho. 
For  the  uses  of  asbestos,  see  page  299. 

Actinolite,  Ca(Mg,Fe)3(SiO3)4. 

Monoclinic,  prismatic  class.  Long  or  short  bladed  crystals,  but 
generally  without  terminal  faces  (Fig.  630) .  Occurs  usually  in  divergent 


FIG.  630. — Actinolite  (dark)  in  talc.     Greiner,  Tyrol. 

or  irregular  columnar,  fibrous,  or  asbestiform  aggregates;  also  in  compact 
granular  masses.  Nephrite  is  a  compact  variety  and  is  included  in 
the  general  term  jade.1 

Perfect  prismatic  cleavage,  at  angles  of  about  56°and  124°.  Hardness 
5  to  6.  Specific  gravity  2.9  to  3.2.  Usually  green  in  color.  Vitreous 
to  silky  luster.  Transparent  to  opaque. 

Ca(Mg,Fe)3(SiO3)4.  Usually  contains  considerable  iron,  and  small 
amounts  of  aluminum  and  sodium.  Fuses  to  a  gray  enamel.  Slightly 
acted  upon  by  acids.  Alters  to  talc,  chlorite,  epidote,  or  to  an  aggregate 
of  serpentine  and  calcite. 

Actinolite  occurs  in  crystalline  schists;  sometimes  in  such  quantities 
that  the  rock  may  be  termed  actinolite  schist.  It  is  often  the  result  of 
contact  metamorphism.  Some  localities  are:  Greiner,  Zillerthal,  Tyrol; 
Norway;  Zoblitz,  Saxony;  lyo,  Japan;  Brome  County,  Quebec;  Bare 
Hills,  Maryland;  Franklin  Furnace,  New  Jersey;  Delaware  and  Chester 

1  Jade  includes  certain  varieties  of  actinolite  and  jadeite,  a  compact  pyroxene  with 
the  formula  NaAl(SiO3)2. 


312 


MINERALOGY 


counties,   Pennsylvania;  Lee  and   Chester,   Massachusetts;   Windham, 
Vermont. 

HORNBLENDE. 

Monoclinic,  prismatic  class.  Prismatic  crystals  with  a  pseudo- 
hexagonal  outline  and  rhombohedral  terminations  are  common.  The 
prism  angles  are  56°  and  124°.  The  common  forms  are  the  unit  prism 
(m),  clinopinacoid  (6),  clinodome  (d),  and  positive  unit  hemiorthodome 


FIG.  631. 


FIG.  632. 


FIG.  633. 


FIG.  634. 


(q)  (Figs.  631,  632,  633,  635,  and  636).  Sometimes  twinned  parallel 
to  orthopinacoid  (Fig.  634).  Occurs  also  in  bladed,  fibrous,  columnar, 
granular,  or  compact  masses. 

Perfect  prismatic  cleavage.  Hardness  5  to  6.  Specific  gravity  2.9 
to  3.3.  Usually  dark  green,  brown,  or  black  in  color;  grayish  green  to 
grayish  brown  streak.  Vitreous  to  silky  luster.  May  be  transparent, 
but  generally  only  translucent  to  opaque. 


FIG.  635. 


FIG.  636. — Hornblende.     Bilin,  Bohemia. 


Chemically,  hornblende  is  an  isomorphous  mixture  of  Ca(Mg,Fe)3 
(Si03)2(Si03)2,  Al2(Mg,Fe)2(A10,)2(SiO,)2,  and  Fe(Mg,Fe)2(FeO3)2 
(SiO3)2.  The  composition  is  strikingly  similar  to  that  of  augite,  see  page 
307.  Some  varieties  contain  small  amounts  of  the  alkalies  and  titanium. 
A  small  amount  of  water  is  usually  present,  which  tends  to  distinguish 
hornblende  from  augite.  Alters  to  chlorite,  epidote,  calcite,  siderite, 
limonite,  and  quartz.  Uralite  is  pyroxene  altered  to  amphibole  with  the 
form  of  the  original  mineral  but  the  cleavage  of  amphibole.  Pyroxene 
commonly  alters  in  this  way  and  the  process  is  termed  uralization. 


DESCRIPTIVE  MINERALOGY 


313 


Hornblende  is  commonly  associated  with  quartz,  feldspar,  pyroxene, 
chlorite,  and  calcite.  It  is  an  essential  or  accessory  constituent  of  many 
plutonic  rocks  such  as  granite,  syenite,  and  diorite;  also  of  hornblende 
schist,  andesite,  phonolite,  gabbro,  and  crystalline  limestones. 

Some  of  the  more  important  localities  are:  Mount  Vesuvius;  Bilin, 
Bohemia;  Pargas,  Finland;  Renfrew  County,  Ontario;  Russel,  Pierre- 
pont,  and  DeKalb,  New  York;  Hawley,  Massachusetts;  Franconia, 
New  Hampshire;  Franklin  Furnace,  New  Jersey. 


LEUCITE,  K2Al2Si4O12. 

Dimorphous,  orthorhombic  and  cubic.  At  ordinary  temperatures 
crystals  are  pseudocubic,  in  that  they  show  what  is  apparently  a  tetra- 
gonal trisoctahedron;  at  times  also  the  cube  and  rhombic  dodecahedron. 
Optically,  the  crystals  consist  of  orthorhombic  twin  lamellae,  which  can 
sometimes  be  recognized  by  the  stria- 
tions  on  the  faces.  Heated  to  a  tem- 
perature of  500°C.,  the  lamellae  disappear 
and  the  crystals  become  isotropic  and 
truly  cubic.  Generally  found  in  well 
developed  and  disseminated  crystals 
(Fig.  637) ;  also  in  rounded  grains. 

Conchoidal  fracture.  Hardness  5.5 
to  6.  Specific  gravity  2.5.  White,  gray, 
yellowish,  or  reddish  in  color.  Vitreous 
to  greasy  luster.  Translucent,  rarely 
transparent. 

K2Al2Si4Oi2.  Sodium  may  replace 
some  of  the  potassium.  Infusible. 
Alters  to  analcite  and  kaolin. 

Leucite  occurs  usually  in  eruptive 
rocks.  The  principal  associates  are  sani- 

dine,  augite,  nephelite,  and  olivine.  Some  localities  are:  Mount  Vesu- 
vius; Laacher  See,  Rhenish  Prussia;  Kaiserstuhl,  Baden;  Saxony;  Brazil; 
Leucite  Hills,  Wyoming;  Magnet  Cave,  Arkansas. 

At  present  leucite  is  of  no  importance  commercially. 

BERYL,  Be3Al2Si6Oi8. 

Hexagonal,  dihexagonal  bipyramidal  class.  Crystals  are  usually 
long  prismatic  and  very  simple  (Fig.  638  and  639).  Rarely  tabular. 
Sometimes  highly  modified,  showing  prisms  and  forms.  Crystals 
are  frequently  striated  vertically  and  may  be  very  large.  Occurs  also 
in  columnar,  granular,  and  compact  masses,  and  in  rounded  grains  and 
masses  in  secondary  deposits. 

Distinct  basal  cleavage.  Conchoidal  to  uneven  fracture.  Hardness 
7.5  to  8;  is  sometimes  substituted  for  topaz  in  the  scale  of  hardness. 


FIG.  637.— Leucite  (light)  in 
basalt.     Tavolato,  Italy. 


314  MINERALOGY 

Specific  gravity  2.6  to  2.8.  Various  shades  of  green,  blue,  yellow,  and 
reddish  in  color;  sometimes  mottled.  Vitreous  luster.  Transparent  to 
translucent. 

There  are  five  important  varieties  of  beryl: 

(1)  Emerald. — Emerald  green  in  color.  Transparent.  Highly  prized 
as  a  precious  stone. 


FIG.  638.— Beryl.     Auburn,  Maine.  FIG.  639. 

(2)  Aquamarine. — Usually  blue  to  sea  green  in  color.     Transparent. 
Used  as  a  gem,  but  not  as  valuable  as  the  emerald. 

(3)  Yellow  or  Golden  Beryl. — Beautiful  golden  yellow  in  color.     Trans- 
parent.    An  attractive  gem  stone. 

(4)  Morganite. — Pale  pink  to  rose  red  in  color.     Transparent.     Used 
as  a  gem. 


FIG.  640. — Beryl  in  quartz.         FIG.  641. — Beryl:  Variety,  emerald. 
Acworth,  New  Hampshire.  Bogota,  Columbia. 

(5)  Common  Beryl. — generally  green,  yellowish,  or  grayish  white  in 
color.  Often  mottled.  Crystals  are  sometimes  extremely  large,  being 
measured  in  feet  and  jtveighing  as  much  as  1,500  kilograms  (Graf ton, 
New  Hampshire). 

Be3Al2(SiO3)6.  Beryllium  may  be  partially  replaced  by  varying 
amounts  of  calcium,  iron,  potassium,  sodium,  and  caesium.  Fuses  with 
great  difficulty,  turning  white  and  cloudy.  Insoluble  in  acids.  Alters 
to  mica  and  kaolin. 


DESCRIPTIVE  MINERALOGY  315 

Commonly  found  in  pegmatite  veins,  gneiss,  mica  schist,  clay  slate, 
limestone,  or  in  secondary  deposits.  The  common  associates  are  quartz 
(Pig.  640),  feldspar,  mica,  topaz,  tourmaline,  cassiterite,  chrysoberyl, 
garnet,  zircon,  and  corundum.  Emeralds  of  good  quality  occur  in 
limestone  at  Muzo,  Columbia  (Fig.  641),  district  of  Ekaterinburg, 
Ural  Mountains; Tyrol; Upper  Egypt;  Alexander  County,  North  Carolina; 
Chaff ee  County,  Colorado.  Morganite  is  found  oh  the  Island  of  Mada- 
gascar and  in  San  Diego  County,  California.  Aquamarine  and  other  gem 
beryls  occur  on  the  Island  of  Elba;  Ireland;  Mursinka,  Ural  Mountains; 
Mitchell  County,  North  Carolina;  in  secondary  deposits'in  Brazil,  Ceylon, 
and  India.  Common  beryl  occurs  in  very  large  crystals  at  Grafton  and 
Acworth,  New  Hampshire;  Royalston,  Massachusetts;  Paris  and  Stone- 
ham,  Maine;  Haddam  and  Litchfield,  Connecticut;  Pennsylvania;  Black 
Hills,  South  Dakota. 

Used  for  gem  purposes  and  as  a  source  of  beryllium  and  its  compounds. 

Feldspar  Group 

The  feldspars  constitute  the  most  abundant  group  of  minerals.  They 
are  very  important  rock  minerals  and,  according  to  Clarke,  make  up 
about  60  per  cent,  of  the  igneous  rocks.  Their  chemical  composition  is 
very  similar  and  may  be  expressed  in  general  by  the  formulas  M'AiSi3O8 
or  M"AlSi2O8,  in  which  the  metal  may  be  potassium,  sodium,  calcium, 
or  more  rarely  barium.  The  feldspars  crystallize  in  the  monocKnic  and 
triclinic  systems,  but  many  of  their  physical  properties  are  strikingly 
similar.  The  prism  angles  are  about  120°.  Hardness  6  to  6.5.  Specific 
gravity  2.55  to  2.75.  The  color  is  usually  white  or  gray,  but  may  also 
be  reddish,  yellow,  or  greenish.  All  feldspars  possess  good  cleavages  in 
two  directions,  that  is,  parallel  to  basal  and  clino-  or  brachypinacoids. 
In  the  case  of  orthoclase  these  cleavages  make  an  angle  of  90°,  but  in  the 
case  of  the  triclinic  members  they  are  inclined,  jheir  angles  differing 
slightly  from  90°. 

The  feldspars  are  important  economic  minerals  and  132,  681  short  tons 
were  produced  in  the  United  States  in  1916;  82  per  cent,  of  the  output 
was  consumed  in  the  ceramic  industries.  The  chief  producing  states  are 
North  Carolina,  Maine,  Maryland,  New  York,  and  Connecticut. 

The  following  feldspars  will  be  described : 

Orthoclase,  KAlSi3O8  Monoclinic 

Microcline,  KalSi3O8  Triclinic 

PLAGIOCLASES 

Albite,  NaAlSi3O8(Ab)  Triclinic 

Labradorite,  AbiAni  to  AbiAns          Triclinic 

Anorthite,  CaAl2Si2O8(An)  Triclinic 


316 


MINERALOGY 


Igneous  rocks  are  commonly  classified  according  to  the  kind  of  feld- 
spar they  contain. 

ORTHOCLASE  (Potash  Feldspar,  Feldspar),  KAlSi3O8. 

Monoclinic,  prismatic  class.  Well  developed  crystals  are  common, 
the  habit  being  usually  prismatic  parallel  to  the  c  axis  (Fig,  642),  tabular 
parallel  to  the  clinopinacoid,  or  square  columnar  and  elongated  parallel 
to  the  a  axis  (Fig.  643).  In  the  latter  case  the  basal  and  clinopinacoids 


FIG.  642.— Or- 
thoclase.  Lincoln 
County,  Nevada. 


FIG.  643.— Ortho- 

clase :  Variety,  sani- 
dine.  Fort  Bayard, 
New  Mexico. 


FIGS.  644  and  645.— Orthoclase 
(left  and  right  Karlsbad  twins).  Fort 
Bayard,  New  Mexico. 


are  about  equally  developed.  The  unit  prism,  positive  hemi-orthodomes, 
a  clinodome,  and  the  basal  and  clinopinacoids  are  the  forms  most  fre- 
quently observed.  Crystals  are  sometimes  highly  modified  and  may  be 
quite  large.  Twinning  is  frequently  observed  according  to  three  laws. 

(1)  Karlsbad  Law. — The  orthopinacqid  acts  as  the  twinning  plane  or 
the  crystallographic  c  axis  may  be  considered  the  twinning  axis.  Irre- 
gular penetration  twins  are  common  (Figs.  644  and  645). 


FIG.  646. 


FIG.  647. 


(2)  Baveno  Law. — The  clinodome  (  CD  a  :  6  :  2c)  is  the  twinning  plane. 
Nearly  square  or  columnar  contact  twins  are  most  common  (Fig.  646). 

(3)  Manebach  Law. — This  law  yields  contact  twins  with  the  basal 
pinacoid  acting  as  the  twinning  and    composition    plane    (Fig.    647). 
This  law  is  not  as  common  as  the  first  two. 

Aside  from  occurring  in  crystals,  orthoclase  is  found  in  cleavable, 
compact,  or  granular  masses,  and  in  irregular  disseminated  grains.  Some 
massive  orthoclase  resembles  jasper  or  flint. 


DESCRIPTIVE  MINERALOGY 


317 


Perfect  basal  and  good  clinopinacoidal  cleavages,  making  an  angle  of 
90°  (Fig.  648).  Conchoidal  to  uneven  fracture.  Hardness  6.  Specific 
gravity  2.5  to  2.6.  Usually  colorless,  white,  gray,  or  reddish,  or  yellow- 
ish; more  rarely  greenish.  Transparent  to  opaque.  Vitreous  to  pearly 
luster. 


FIG.  648. — Orthoclase  show- 
ing rectangular  cleavage. 


FIG.  649.— Orthoclase:  Variety, 
sanidine,  in  trachyte.  Drachen- 
fels,  Rhine  Valley. 


There  are  three  important  varieties: 

(1)  Adularia. — This   variety   occurs   usually   in   white   or   colorless 
crystals,  which  may  be  transparent  or  slightly  cloudy.     It  frequently 
possesses  an  excellent  opalescence.    It  is  then  termed  moonstone  and  is  used 
for  gem  purposes.     Usually  found  in  cracks  and 

veins  in  gneiss  and  mica  schist. 

(2)  Sanidine. — Occurs  in  glassy,  transparent 
or  translucent  crystals,  and  is  sometimes  called 
glassy  feldspar.     Generally   colorless,  white,  or 
gray.     Tabular  and  square  habits  and  Karlsbad 
twins  are  very  common.     Characteristic  of  erup- 
tive  rocks,    especially   rhyolite,    trachyte,    and 
phonolite  (Fig.  649). 

(3)  Ordinary  or  Common  Orthoclase. — Gener- 
ally more  or  less  dull  in  color,  yellowish,  flesh 
red,  dark  red,  or  greenish.     Occurs  in  well  de- 
veloped  crystals  and  in  cleavable  or  compact 
granular    masses.      Very    common    in    granite, 
syenite,  gneiss,  and  pegmatites. 

KAlSi3O8.  Often  contains  some  sodium.  Fuses  with  difficulty. 
Insoluble  in  acids.  Alters  to  kaolinite,  muscovite,  and  epidote.  Occurs 
as  a  pseudomorph  after  analcite  and  leucite. 

Orthoclase  is  a  very  common  mineral.  It  is  especially  characteristic 
of  such  plutonic  rocks  as  granite  and  sj-enite,  and  in  pegmatite  dikes  cut- 
ting them.  It  is  also  an  important  constituent  of  certain  eruptive  and 


FIG.  6 5 0.— Orthoclase 
intergrown  with  quartz 
(graphic  granite).  Bedford, 
N.  Y.  (After  Basting 


318  MINERALOGY 

metamorphic  rocks,  for  example,  rhyolite,  trachyte,  phonolite,  porphyry, 
gneiss,  and  various  schists.  Not  infrequently  it  occurs  in  some  sand- 
stones and  conglomerates.  The  most  common  associates  of  orthoclase 
are  muscovite,  biotite,  quartz  (Fig.  650),  tourmaline,  the  other  felds- 
pars, hornblende,  apatite,  zircon,  and  beryl.  It  occurs  widely  distributed 
and  is  frequently  considered  the  most  abundant  of  the  silicate  minerals. 
A  few  localities  for  excellent  crystals  are:  the  St.  Gothard  district,  Switzer- 
land; Mount  Vesuvius;  Karlsbad,  Bohemia;  Striegau,  Silesia;  Norway; 
Ceylon;  Perth,  Quebec;  Bedford,  Ontario;  Paris,  Maine;  Acworth,  New 
Hampshire;  Haddam,  Connecticut;  St.  Lawrence  County,  New  York; 
Mount  Antero,  Chaffee  County,  Colorado.  Massive  varieties  are  found 
at  Bedford,  Ontario;  Georgetown  and  Brunswick,  Maine;  Crown  Point 
and  elsewhere,  New  York;  also  in  Pennsylvania,  Maryland,  Virginia, 
Minnesota,  and  Massachusetts. 

The  feldspar  of  commerce  is  principally  orthoclase  or  microcline,  or 
an  intergrowth  of  both.  It  is  used  chiefly  as  a  constituent  of  the  glaze 
of  porcelain,  china,  or  enamel  ware,  and  as  a  flux  in  the 
manufacture  of  emery  and  other  abrasive  wheels. 
Small  quantities  are  also  used  in  opalescent  glass,  arti- 
ficial teeth,  scouring  soap,  and  paint  fillers.  Moon- 
stone is  used  as  a  gem. 


MICROCLINE,    KALSi3O8. 

triclinic,  pinacoidal  class.  Crystals  resemble  very 
closely  those  of  orthoclase  in  habit  (Fig.  651),  angles, 

FIG.  651.— Mi-  crystal  forms,  and  twinning.  The  angle  between  the 
crociine:  Variety,  basal  and  brachypinacoids  differs  slightly  from  90°, 
Pike's  Peak,  Colo-  being  about  90°  30'.  Crystals  are  frequently  large 
rado-  and  although  apparently  simple  individuals,  they  are 

in  reality  usually  polysynthetic  twins  according  to  the 
ablite  and  pericline  laws — see  page  320 — so  characteristic  of  ablite  and 
other  triclinic  feldspars.  Accordingly  basal  sections  of  microcline  show 
under  the  microscope  a  characteristic  grating  or  gridiron  structure.  Also 
occurs  in  cleavable  and  compact  granular  masses. 

Basal  and  brachypinacoidal  cleavages.  Uneven  fracture.  Hardness 
6  to  6.5.  Specific  gravity  2.54  to  2.57.  Vitreous  luster,  inclining 
to  pearly  on  the  basal  pinacoid.  White,  yellowish,  gray,  green,  or 
red  in  color.  Green  varieties — often  bright  verdigris  green — are  called 
amazonite  or  amazonstone.  Transparent  to  translucent. 

KAlSi3O6.  Usually  contains  some  sodium.  The  chemical  properties 
are  the  same  as  for  orthoclase. 

The  occurrence  of  microcline  is  very  similar  to. that  of  orthoclase. 
Microcline  is,  however,  not  common  in  eruptive  rocks.  Smoky  quartz 
and  topaz  are  typical  associates.  Intergrowths  with  orthoclase,  albite, 
and  the  other  feldspars  are  common.  Some  localities  are:  Striegau, 


DESCRIPTIVE  MINERALOGY 


319 


Silesia;   Arendal,   Norway;   Ural  Mountains;   Greenland;   Pike's   Peak 
district,  Colorado. 
Amazonstone  is  cut  and  polished  for  gem  and  ornamental  purposes. 


Plagioclase  Feldspars 

These  Feldspars  are  sometimes  called  the  soda-lime  feldspars.  They 
crystallize  in  the  triclinic  system,  forming  an  isomorphous  series  with 
albite  and  anorthite  as  the  end  members.  The  chemical  composition 
of  the  various  members  of  this  series  may  be  indicated  as  follows: — 

Albite,  NaAlSi308 (Ab), 

Olgioclase,     Ab AbaAn, 

Andesine,    Ab3An AbiAni 

Labradorite,  AbiAn! AbiAns 

Bytownite,  AbiAn3 An, 

Anthorite,  CaAl2Si2O8 (An). 

These  feldspars  possess  good  cleavages  parallel  to  the  basal  and  brachy- 
pinacoids,  which  are  inclined  to  each  other  at  angles  of  about  86°.  This 
inclined  or  oblique  cleavage  serves  to  differentiate  these  feldspars,  the 
plagioclases,  from  orthoclase  which  possesses  a  rectangular  cleavage. 

The  following  table  shows  clearly  the  progressive  changes  in  the 
physical  and  chemical  properties  of  the  various  members  of  this  group. 


Extinction 

Name 

Compo- 
sition 

Per  cent, 
of 

Anorthite 

SiOz 

CaO 

NazO 

AlzO, 

Specific 
Gravity 

Angles 

Cleavage 
Angles 

Basalt 

Brachy 

Albite 

0.0 

68.6 

11.8 

19.6 

2.605 

*H« 

19° 

86°  24' 

Ab 

Oligoclase 

26.0. 

61.9 

5.2 

8.7 

24.2 

2.659 

1° 

4H 

86°  32' 

AbiAni 

Andesine 

V 

51.5 

55  .4 

10.4 

5.7 

28.5 

2.694 

-5° 

-16° 

86°  14' 

AbiAni 

Labradorite 

76.1 

49.1 

15.3 

2.8 

32.8 

2.728 

-17^° 

-29K° 

86°  4' 

AbiAni 

Bytownite 

96.0 

46.6 

17.4 

1.6 

34.4 

2.742 

-27K° 

-33H° 

— 

An 

' 

Anorthite 

100.0 

43.0 

20.1 

36.9 

2.765 

-37° 

-36° 

85°  50' 

The  intermediate  members  are  important  constituents  of  many 
igneous  rocks  and  more  common  than  either  albite  or  anorthite.  They 
are  rarely  well  crystallized,  but  can  usually  be  recognized  by  the  stria- 
tions  on  the  basal  pinacoid,  due  to  multiple  twinning  according  to  the 
albite  law.  Only  albite,  labradorite,  and  anorthite  will  be  described. 

ALBITE   (Soda  Feldspar)    NaAlSi3O8. 

Triclinic,  pinacoidal  class.  Crystals  are  usually  not  large  and  often 
similar  in  development  to  those  of  orthoclase  (Figs.  652  and  653).  They 


320 


MINERALOGY 


may  also  be  tabular  and  elongated  parallel  to  the  b  axis  (Fig.  656). 
Twins  are  very  common,  single  individuals  being  rare.  There  are  two 
important  laws. 

(1)  Albite  Law. — This  involves  the  brachypinacoid  acting  as  the 
twinning  plane,  and  yields  simple  contact  and  repeated  twins  (Figs. 
654  and  655).  The  polysynthetic  twins  according  to  this  law  show 
striations  on  the  basal  pinacoid  which  extend  parallel  to  the  edge  between 
the  basal  and  brachypinacoids. 


FIG.  652. 


FIG.  653. 


FIG.  654. 


FIG.  655. 


(2)  Peridine  Law. — The  b  axis  acts  as  the  twinning  axis  (Fig.  657). 
Contact  and  polysynthetic  twins  are  observed,  the  latter  being  character- 
ized by  striations  on  the  brachypinacoid. 

Albite  also  occurs  in  lamellar  and  granular  masses,  the  laminae  being 
often  curved  and  divergent. 

Perfect  basal  and  brachypinacoidal  cleavages,  inclined  at  86°  24' 
Uneven  fracture.  Hardness  6  to  6.5.  Specific  gravity  2.6.  Usually 
colorless  or  gray;  rarely  colored.  Transparent  to  translucent.  Some 
varieties  show  a  bluish  opalescence  and  are  called  moonstone. 


FIG.  656. 


FIG.  657. 


NaAlSij08.  Generally  contains  some  potassium  and  calcium.  Fuses 
to  a  colorless  or  white  glass.  Colors  the  flame  yellow.  Not  acted  upon 
by  acids. 

As  a  rock  mineral,  albite  is  not  as  abundant  as  the  other  plagioclases. 
It  occurs,  nevertheless,  in  many  gneisses  and  other  crystalline  schists, 
also  in  granite,  diorite,  trachyte,  and  other  eruptive  rocks;  more  rarely 
in  limestone  and  dolomite.  Frequently  found  in  pegmatite  veins,  but 
also  in  cracks  and  crevices.  Some  of  the  associates  of  albite  are  chlorite, 
titanite,  adularia,  axinite,  beryl,  tourmaline,  quartz,  chrysoberyl,  and 


DESCRIPTIVE  MINERALOGY 


321 


apatite.  It  occurs  often  intergrown  with  orthoclase  or  microcline,  and  is 
then  known  as  perthite  (Fig.  658). 

Some  important  localities  are:  the  St.  Gothard  district,  Switzerland; 
various  places  in  the  Tyrol;  Rauris,  Salzburg;  Dauphine,  France;  Ural 
Mountains;  Paris,  Maine;  Haddam,  and  Branchville,  Connecticut; 
Chesterfield,  Massachusetts;  Pike's  Peak,  Colorado;  Amelia  Court 
House,  Virginia  (Fig.  659). 

Moonstone  is  often  used  for  gem  purposes. 


FIG.  658. — Perthitic   intergrowth  of  microcline  and 
albite.     Georgetown,  Maine.      (After  Bastin.) 


FIG.  659. — Albite.     Amelia 
Court  House,  Virginia. 


LABRADORITE  (Lime-soda  Feldspar),  AbiAni  to  AbjAn3. 

Triclinic,  pinacoidal  class.  Well  developed  crystals  are  rare.  In 
habit  they  are  usually  tabular  to  the  brachypinacoid.  The  twinning  is 
the  same  as  for  albite.  Generally  observed  in  cleavable,  granular,  or 
crypt ocrystalline  masses. 

Perfect  basal  and  brachypinacoidal  cleavages,  making  an  angle  of 
86°4/.  Uneven  fracture.  Hardness  6  to  6.5.  Specific  gravity  2.7. 
Gray,  brown,  or  greenish  in  color.  Often  shows  a  beautiful  play  of  yel- 
lowish, bluish,  greenish,  or  reddish  colors  on  the  brachypinacoid.  This 
labradorescence  is  due  to  a  fine  lamellar  structure  or  to  microscopic 
inclusions,  or  to  both.  Translucent. 

AbiAni  to  AbiAn3.  Fuses  to  a  colorless  or  white  glass.  Colors  the 
flame  yellow.  Decomposed  with  difficulty  by  hydrochloric  acid. 

Occurs  in  basic  igneous  rocks,  such  as  gabbro,  norite,  basalt,  diabase, 
and  andesite.  Found  on  Mount  Aetna;  in  Transylvania;  Sweden;  Green- 
land; varieties  showing  an  excellent  play  of  colors  are  common  on  the 
21 


322 


MINERALOGY 


coast  of  Labrador,   also  on   the  Isle  of  St.  Paul;  in  the  Adirondack 
Mountains,  New  York;  Wichita  Mountains,  Arkansas;  and  elsewhere. 

Varieties  showing  a  good  play  of  colors  are  used  for  ornamental  and 
decorative  purposes.  They  are  sometimes  termed  labrador  spar. 

Anorthite  (Lime  Feldspar),  CaAl2Si2O8. 

Triclinic,  pinacoidal  class.  Crystals  are  usually  prismatic  parallel 
to  the  c  axis,  or  tabular  parallel  to  the  basal  pinacoid;  often  very  com- 
plex. Twins  occur  according  to  the  laws  common  on  albite.  Also 
observed  in  cleavable,  compact,  and  lamellar  masses. 

Perfect  basal  and  brachypinacoidal  cleavages,  inclined  at  an  angle  of 
85°  50'.  Conchoidal  to  uneven  fracture.  Hardness  6  to  6.5.  Specific 
gravity  2.7  to  2.8.  Commonly  white,  colorless,  or  grayish;  more  rarely 
bluish,  yellowish,  or  reddish.  Vitreous  luster,  inclining  to  pearly  on  the 
cleavages.  Transparent  to  translucent. 

CaAl2Si2O8.  Usually  contains  small  amounts  of  sodium  and  at  times 
of  potassium,  magnesium,  and  iron.  Fuses  with  difficulty  to  a  colorless 
glass.  Decomposed  by  hydrochloric  acid  with  a  separation  of  gelati- 
nous silica. 

Anorthite  occurs  as  an  important  constituent  of  basic  igneous  rocks, 
such  as  gabbros,  diorites,  and  basalts;  also  as  a  contact  mineral  and  in 
meteorites.  Excellent  crystals  are  found  on  Mount  Vesuvius;  Island  of 
Miyake,  Japan;  Iceland;  Monzoni  district,  Tyrol;  Transylvania;  Ural 
Mountains;  Franklin  Furnace,  New  Jersey. 


SCAPOLITE  (Wernerite),  nNa4Al3Si9O24Cl  +  mCa4Al6Si6O25. 
Tetragonal,    tetragonal    bipyramidal    class.     Commonly    as    thick 
coarse,    prismatic    crystals,    often    large  with  dull  and  uneven  faces. 


FIG.  660. 


Fia.  661. — Scapolite.     Ottawa 
County,  Quebec. 


FIG.  662. 


Crystals  sometimes  appear  as  though  partially  fused.  The  common 
forms  are  the  prisms  (m  and  a)  and  bipyramids  (o  and  d)  of  the  first 
and  second  orders;  more  rarely  the  bipyramid  of  the  third  order  (s) 
is  observed  (Figs.  660  and  661).  Occurs  also  in  fibrous,  coarse  to  fine 
granular,  columnar,  and  compact  masses. 

Prismatic  cleavage.     Conchoidal  fracture.     Hardness  5  to  6.     Spe- 


DESCRIPTIVE  MINERALOGY 


323 


cific  gravity  2.6  to  2.8.  Colorless,  white,  gray,  greenish,  bluish,  or  reddish. 
Vitreous  to  greasy  luster.  Translucent. 

The  composition  varies  greatly  between  marialite,  Na4Al3Si9O24Cl, 
and  meionite,  Ca4Al6Si6O25.  Some  scapolites  are  readily  decomposed 
by  hydrochloric  acid.  All  are  quite  easily  fusible  with  intumescence. 
The  scapolites  alter  to  kaolin,  jade,  epidote,  muscovite,  biotite,  albite, 
and  various  zeolites. 

Commonly  the  result  of  metamorphism,  and  frequently  found  in 
granular  limestones  near  the  contact  with  igneous  rocks;  also  in  crystalline 
schists  and  volcanic  ejectamenta.  Typical  associates  are  pyroxenes, 
amphiboles,  apatite,  garnet,  titanite,  zircon,  and  biotite.  Some  localities 
are:  Arendal,  Norway;  Pargas,  Finland;  Laacher  See,  Rhenish  Prussia; 
Mount  Vesuvius;  Ripon  and  Grenville,  Quebec,  and  various  places  in 
Ontario,  Canada;  Bolton,  Massachusetts;  various  places  in  northern  New 
York;  Franklin  Furnace,  New  Jersey. 

Scapolite  is  not  important  commercially. 

TITANITE  (Sphene),  CaTiSiO5. 

Monoclinic,  prismatic  class.  The  crystal  habit  varies  greatly. 
Disseminated  crystals  are  generally  wedge  or  envelope  shaped,  while 
attached  crystals  are  apt  to  be  tabular  or  prismatic  (Figs.  663,  664,  and 


FIG.  663. 


FIG.  664. 


FIG.  665. — Titanite. 
Arendal,    Norway. 


665).  Occurs  also  in  compact  or  lamellar  masses,  and  in  disseminated 
grains. 

Prismatic  and  domatic  cleavages.  Conchoidal  fracture.  Hardness 
5  to  5.5.  Specific  gravity  3.4  to  3.6.  Yellow,  green,  brown,  reddish 
brown,  red,  or  black  in  color.  Vitreous  luster,  inclining  to  adamantine. 
Transparent  to  opaque. 

CaTiSiO5.  Commonly  considered  as  the  calcium  salt  of  the  dimeta- 
silicic  acid,  H2Si2O5,  in  which  one  atom  of  silicon  has  been  replaced  by 
titanium.  May  also  contain  some  iron  or  manganese.  Fuses  with  in- 
tumescence on  the  edges  to  a  dark  colored  glass.  Only  partially  decom- 
posed by  hydrochloric  acid,  completely  by  sulphuric  and  hydrofluoric 
acids.  Alters  to  rutile,  brookite,  or  ilmenite. 


324  MINERALOGY 

Titanite  occurs  disseminated  as  an  important  accessory  constituent 
of  many  igneous  rocks,  especially  in  hornblende  granite,  syenite,  nephe- 
line  syenite,  trachyte,  phonolite,  and  diorite;  also  in  crystalline  schists 
and  granular  limestones.  It  is  found  attached  in  the  cracks  and  cavities 
in  granite,  gneiss,  and  various  schists.  The  common  associates  are  the 
amphiboles,  pyroxenes,  apatite,  zircon,  scapolite,  chlorite,  feldspars, 
quartz,  and  various  iron  minerals.  Some  localities  are:  Laacher  See, 
Rhenish  Prussia;  many  places  in  Switzerland  and  Tyrol,  especially  St. 
Gothard,  Tavetsch,  and  Zillerthal;  Arendal,  Norway;  Ala,  Piedmont; 
Ural  Mountains;  Grenville,  Quebec,  and  Eganville,  Renfrew  County, 
Ontario,  Canada;  Sandford,  Maine;  Bolton  and  Lee,  Massachusetts; 
various  places  in  Lewis,  Orange,  and  other  counties,  New  York;  Franklin 
Furnace,  New  Jersey;  Magnet  Cove,  Arkansas. 

The  clear,  green,  yellow,  or  brownish  varieties  are  used  for  gem  pur- 
poses. They  are  very  brilliant,  possess  an  excellent  adamantine  luster, 
but  are  comparatively  soft. 

Zeolites 

This  group  contains  several  important  secondary  minerals,  which 
are  hydrated  silicates  of  aluminum,  calcium,  sodium,  and  potassium. 
They  are  commonly  found  in  good  crystals,  have  comparatively  low 
specific  gravities,  2  to  2.4,  and  are  rather  soft,  3.5  to  5.  Although  gen- 
erally colorless  and  transparent  or  translucent,  they  may  be  light  colored, 
'due  to  the  presence  of  pigments.  All  zeolites  are  readily  decomposed  by 
hydrochloric  acid,  and  many  gelatinize  on  evaporation.  They  result 
from  the  decomposition  of  such  minerals  as  nephelite,  leucite,  sodalite, 
and  the  feldspars.  They  are  never  found  disseminated  but  always  in 
cracks,  crevices,  or  cavities  in  basic  igneous  rocks,  such  as  basalt,  diabase, 
and  phonolites;  more  rarely  in  granite  and  mica  schist.  Their  common 
associates  are  calcite,  datolite,  and  pectolite. 

Natrolite  (Needle  Zeolite},  Na2Al(AlO)(SiO3)3.2H2O. 

Orthorhombic,  bipyramidal  class.  Crystals  are  slender  prismatic 
and  nearly  square  in  cross-section;  also  acicular  and  arranged  in  radial 
or  interlacing  groups  (Fig.  666).  Occurs  also  in  fibrous,  granular, 
or  compact  masses. 

Perfect  prismatic  cleavage.  Hardness  5  to  5.5.  Specific  gravity  2.2 
to  2.3.  Colorless  or  white;  also  reddish,  yellowish,  or  greenish.  Trans- 
parent to  translucent.  Vitreous  to  silky  luster. 

Na2Al(AlO)(SiO3)3.2H2O.  May  contain  some  calcium  and  potas- 
sium. Fuses  easily  to  colorless  glass.  Gelatinizes  with  acids.  Yields 
water  in  a  closed  tube. 

Occurs  in  cracks  and  cavities  in  basic  igneous  rocks.  Common  asso- 
ciates are  chabazite,  analcite,  apophyllite,  stilbite,  calcite,  and  datolite. 

Some  notable  localities  are:  Teplitz  and  Aussig,  Bohemia;  Fassathal, 


DESCRIPTIVE  MINERALOGY 


325 


Tyrol;  Hohentwiel  and  Kaiserstuhl,  Baden;  Nova  Scotia;  Bergen  Hill, 
New  Jersey;  Lake  Superior  copper  district. 


FIG.  666. — Natrolite.     Paterson,  New  Jersey. 

ANALCITE,  Na2Al2(Si03)4.2H2O. 

Cubic,  hexoctahedral  class.  Generally  in  well  developed  tetragonal 
trisoctahedrons  (Fig.  667);  sometimes  in  combination  with  the  cube 
(Fig.  668).  Crystals  are  usually  quite  small,  although  some  measuring 
a  foot  in  'diameter  have  been  observed.  Occurs  also  in  compact, 
granular,  or  earthy  masses. 

Uneven  to  conchoidal  cleavage.  Hardness  5  to  5.5.  Specific  gravity 
2.2  to  2.4.  Colorless  or  white;  also  yellowish,  reddish,  or  greenish. 
Vitreous  luster.  Transparent  to  nearly  opaque. 


FIG.  667. — Analcite  (tetragonal 
trisoctahedron).  Lake  Superior 
Copper  District. 


FIG.  668. 


Na2Al2(Si03)4.2H2O.  Chemically  it  is  closely  related  to  soda  leucite. 
Fuses  to  a  colorless  glass.  Gelatinizes  with  acids. 

Analcite  is  commonly  a  secondary  mineral  occurring  with  the  other 
zeolites,  calcite,  datolite,  native  copper,  magnetite,  and  prehnite  in 
basalt,  diabase,  granite,  and  gneiss.  Some  localities  are:  the  Cyclopean 
Islands,  near  Sicily;  Tyrol;  Bohemia;  Iceland;  various  places  in  Nova 


326 


MINERALOGY 


Scotia;  Bergen  Hill,  New  Jersey;  Lake  Superior  copper  district;  Table 

Mountain,  Colorado. 

APOPHYLLITE,  H14K2Ca8(SiO3)i6.9H20, 

Tetragonal,  ditetragonal  bipyramidal  class.  Crystals  may  be  (1) 
long  and  square  prismatic  (Fig.  669),  (2)  pseudocubical  (Fig.  671), 
(3)  pyramidal  (Fig.  672),  or  (4)  thin  tabular  (Fig.  670).  The  most 
general  combination  consists  of  the  prism  of  the  second  order  (a),  unit 
bipyramid  of  the  first  order  (o),  and  the  basal  pinacoid  (c).  The  prism 
faces  are  often  brilliant  and  striated  vertically,  those  of  the  basal  pinacoid 
dull  or  rough,  while  the  bipyramidal  faces  may  be  uneven.  Occurs  also 
massive,  and  in  granular  and  lamellar  aggregates. 

Perfect  basal  cleavage.  Uneven  fracture.  Hardness  4.5  to  5.  Spe- 
cific gravity  2.3  to  2.4.  Generally  colorless  or  white,  also  green,  yellow, 
or  reddish.  Vitreous  to  pearly  luster,  with  fish-eye  opalescence  on  basal 
pinacoid.  Usually  transparent,  rarely  nearly  opaque. 


FIG.  670. 


FIG.  669. 


FIG.  671. — 'Apophyllite.     Paterson, 
New  Jersey. 


FIG.  672. 


i6.9H2O.  The  composition  is  somewhat  uncertain. 
Small  amounts  of  fluorine  may  be  present.  Exfoliates  and  fuses  easily 
to  a  white  enamel,  coloring  the  flame  violet.  Decomposed  by  hydro- 
chloric acid  with  a  separation  of  silica.  Alters  to  calcite,  pectolite,  and 
kaolin. 

Occurs  as  a  secondary  mineral  in  cracks  and  cavities  in  basic  igneous 
rocks,  also  in  granite  and  gneiss.  Common  associates  are  natrolite, 
analcite,  datolite,  prehnite,  pectolite,  native  copper,  and  calcite. 
Found  in  the  Harte  Mountains;  Freiberg,  Saxony;  Tyrol;  Sweden; 
Iceland;  Greenland;  Nova  Scotia;  Bergen  Hill,  New  Jersey;  Table 
Mountain,  Colorado;  Lake  Superior  copper  district;  New  Almaden, 
California. 

STILBITE  (Desmine),  (Ca,Na2)Al2Si6Oi6.6H2O. 

Monoclinic  prismatic  class.  Simple  crystals  are  unknown,  usually 
as  tabular  penetration  twins.  Very  commonly  several  twin  crystals 


DESCRIPTIVE  MINERALOGY 


327 


are  arranged  nearly  parallel  forming  sheaf -like  aggregates  (Fig.  673). 
Occurs  also  in  radial  or  globular  aggregates. 

Clinopinacoid  cleavage.  Uneven  fracture.  Hardness  3  to  4.  Spe- 
cific gravity  2.1  to  2.2.  Vitreous  to  pearly  luster.  Transparent  to  trans- 
lucent. Colorless  or  white,  also  brown,  yellow,  reddish. 


FIG.  673. — Stilbite.     Viesch,  Switzerland. 

(Ca,Na2)Al2Si6Oi6.6H2O.  May  contain  some  potassium.  Exfoliates, 
swells  up,  and  fuses  to  a  white  glass.  Decomposed  by  hydrochloric  acid 
with  a  separation  of  silica. 

Stilbite  occurs  with  other  zeolites,  datolite,  and  calcite,  in  cavities  in 
amygdaloidal  basalts  and  related  rocks;  also  in  granites  and  crystalline 
schists  and  in  ore  deposits.  Some  localities  are:  Tyrol;  Sweden;  Iceland; 
Switzerland;  Kilpatrick,  Scotland;  Nova  Scotia;  Bergen  Hill,  New  Jersey; 
Lake  Superior  copper  district;  Table  Mountain,  Colorado. 


FIG.  674. 


FIG.  675. — Chabazite 
(twinned).  Paterson, 
New  Jersey. 


FIG.  676. 


CHABAZITE,  CaAl2Si6Oi6.8H2O. 

Hexagonal,  ditrigonal  scalenohedral  class.  Generally  in  cube-like 
rhombohedrons  (Fig.  674).  Sometimes  crystals  are  complex  (Fig.  676) 
or  twinned  (Fig.  675).  Occurs  also  in  compact  masses. 

Rhombohedral  cleavage.  Uneven  fracture.  Hardness  4  to  5.  Spe- 
cific gravity  2.1  to  2.2.  Colorless,  white,  reddish,  yellowish,  or  brown. 
Vitreous  luster.  Transparent  to  translucent. 

CaAl2Si6Oi6.8H2O.  Composition  varies  considerably.  May  contain 
potassium  and  sodium  replacing  some  of  the  calcium.  Fuses  with 


328  MINERALOGY 

intumescence  to  a  nearly  opaque,  blebby  glass.     Decomposed   by  hydro- 
chloric acid  with  a  separation  of  silica. 

Associated  with  the  other  zeolites,  it  generally  occurs  in  cavities  in 
basalts,  phonolites,  and  related  rocks.  Some  localities  are:  'Giant's 
Causeway,  Ireland;  Aussig,  Bohemia;  Faro  Island,  Sweden;  Greenland; 
Iceland;  Nova  Scotia;  Bergen  Hill,  New  Jersey;  Somerville,  Massa- 
chusetts; Table  Mountain,  Colorado. 


CHAPTER  XV 


GEMS  AND  PRECIOUS  STONES 

A  considerable  number  of  minerals  occur  with  beautiful  colors,  some 
are  transparent  and  exceedingly  brilliant,  while  others  possess  a  pleasing 
luster  or  sheen.  Minerals  of  this  character  have,  from  the  earliest  times, 
been  eagerly  sought  after  for  personal  adornment  and  ornamentation. 
They  constitute  what  we  call  gems  and  precious  stones.  In  fact,  it  is 
well  known  that  among  primitive  peoples  many  of  these  gem  minerals 
were  supposed  to  possess  peculiar  properties.  Some  were  believed  to  bring 

good  luck  to  the  wearer,  while  others  were 
thought  to  be  useful  in  warding  off  or  cur- 
ing certain  diseases. 

Characteristics  of  Gems. — The  out- 
standing qualities  of  a  gem  are  (1)  splendor 
or  beauty,  (2)  durability,  (3)  rarity,  and  (4) 
fashion.  The  beauty  of  a  gem  depends 
upon  its  transparency  or  clarity,  brilliancy, 
color,  luster,  and  fire.  In  some  cases  these 
qualities  are  seen  to  best  advantage  only 
when  the  stone  is  cut  and  polished.  Red 
and  blue  diamonds,  for  example,  embody  all 
of  these  qualities  to  a  marked  extent. 
Sometimes  the  beauty  of  a  gem  does  not 
^pend  upon  all,  but  only  upon  several,  of 
the  the  above  properties.  Thus,  the  beauty  of 
the  ruby  is  the  result  of  its  excellent  color, 
luster,  and  transparency.  It  is  however 
almost  totally  lacking  in  fire.  The  opal  is 

attractive  principally  on  account  of  its  fascinating  play  of  colors.  In 
the  case  of  turquois,  the  beauty  depends  mainly  upon  a  pleasing  color. 
Water  white  diamonds  are  exceptionally  beautiful,  but  they  are  devoid 
of  color,  their  splendor  being  due  to  their  brilliancy,  luster,  and  fire. 

Many  minerals  may  be  pleasing  to  the  eye,  but  yet  not  be  very  serv- 
iceable as  gems  because  of  their  inferior  hardness.  They  do  not  wear 
well;  that  is,  they  lack  durability.  In  order  to  serve  to  advantage  as  a 
gem,  a  mineral  must  be  hard.  It  must  resist  abrasion.  When  worn  on 
the  hand,  a  stone  is  not  only  subject  to  the  action  of  the  ever  present 
dust,  which  consists  mainly  of  finely  divided  quartz  particles  and  hence 

329 


logy  and  petrography  in 
University  of  Marburg  (1884- 
1918).  Distinguished  authority 
on  gems  and  precious  stones. 


330  MINERALOGY 

is  hard,  but  it  is  also  subject  to  sudden  shocks  and  knocks.  Soft  stones, 
even  though  they  may  take  a  beautiful  polish  and  possess  other  neces- 
sary gem  properties,  become  dull  and  worthless  in  a  very  short  time. 
Stones  of  such  inferior  hardness  serve  fairly  well  in  pins  and  brooches. 
A  gem  to  be  durable  must  therefore  be  hard,  preferably  harder  than  quartz. 
In  fact,  durability  plays  a  prominent  role  in  the  classification  of  gems. 
Those  which  are  generally  classed  as  the  distinctly  precious  stones' — 
diamond,  emerald,  ruby,  sapphire — all  possess  superior  hardness,  being 
decidedly  harder  than  quartz.  Soft  gem  minerals  are  generally  regarded 
as  semi-precious. 

While  durability  is  a  fundamental  quality  of  a  gem,  frequency  of  oc- 
currence has  much  to  do  with  determining  the  value  of  a  mineral  for  gem 
purposes.  Many  minerals  occur  rather  abundantly  in  nature,  but  only 
rarely  are  some  of  them  found  in  such  condition  as  to  warrant  their  use 
as  gems.  Thus,  the  mineral  beryl  is  fairly  common.  It  occurs  in  large 
crystals,  some  of  which  weigh  several  tons,  but  the  colors  are  then  usually 
dull,  and  the  crystals  are  not  transparent.  The  green  transparent 
variety,  called  the  emerald,  is  however  seldom  found  and  is  accordingly 
very  highly  prized.  There  are  other  transparent  varieties  of  beryl, 
such  as  golden  beryl  and  aquamarine,  but  these  are  more  frequently 
found  and  are  not  as  valuable  as  the  rarer  emerald.  Other  things  being 
equal,  the  rarer  the  stone,  the  greater  its  value,  for  there  are  many  people 
who  will  always  desire  that  which  is  rare  and  exceptional  and  be  willing  to 
pay  enormous  prices  in  order  to  obtain  those  gems  which  others  cannot 
afford. 

Fashion  and  style  exert  an  enormous  influence  upon  the  favor  with 
which  a  gem  is  received.  Indeed,  it  frequently  happens  that  as  the  result 
of  a  change  in  fashion  or  style,  an  excellent  gem  mineral — excellent  with 
respect  to  the  various  properties  referred  to  above — is  suddenly  discarded 
for  some  new  and  perhaps  inferior  stone.  During  the  last  thirty  years 
many  stones  have  thus  come  into  favor,  most  of  which  are  of  bright  color. 
Hence,  the  number  of  minerals  which  are  to  be  counted  as  gems  is  subject 
to  change,  the  tendency  being  toward  an  extension  of  the  list. 

List  of  Gems. — The  following  tabulation  contains  the  minerals,  de- 
scribed in  this  text,  which  are  used  as  gems.  In  each  case  the  page  is 
indicated  where  the  mineral  has  been  fully  described.  Where  special 
terms  have  been  assigned  to  varieties  of  gem  quality,  these  are  also  given. 

Diamond,  188 

Beryl,  313  (Emerald,  Aquamarine,  Yellow  or  Golden  Beryl,  Morganite) 

Corundum,  228    (Ruby,  Sapphire,  White  Sapphire,  Golden  Sapphire,  Oriental  Emer- 
ald, Oriental  Topaz,  Oriental  Amethyst] 
Topaz,  283  (Precious  Topaz) 

Spinel,  267  (Ruby  Spinel,  Rubicelle,  Blue  Spinel) 

Garnet,  290  to  293 

Grossularite  (Hessonite,  Cinnamon  Stone) 


GEMS  AND  PRECIOUS  STONES 


331 


Pyrope  (Cape  Ruby,  Arizona  RuJyy) 
Spessartite 

Almandite  (Carbuncle,  Rhodolite} 
Uvarovite 

Andradite  (Topazolite,  Demantoid) 
Tourmaline,  284     (Rubellite) 
Olivine,  289  (Peridot) 

Zircon,  225  (Hyacinth,  Jacinth,  Jargon) 

Chrysoberyl,  271     (Alexandrite,  Cat's  Eye,  Cymophane) 
Opal,  232  (Precious  Opal,  White  Opal,  Black  Opal,  Fire  Opal) 

Quartz,  220  (Rock   Crystal,   Amethyst,   Rose  Quartz,  Smoky  Quartz,  Cairngorm 

Stone,  False  Topaz,  Spanish  Topaz,  Citrine,  Aventurine,  Ruti- 
lated  Quartz,   Cat's  Eye,  Tiger's  Eye,  Chalcedony,  Carnelian, 
Sard,  Chrysoprase,  Heliotrope,  Bloodstone,  Agate,  Onyx) 
Turquois,  276 

Jade,  311  (Nephrite,  Jadeite) 

Feldspar,  315 

Orthoclase  (Moonstone),  317 
Microcline  (Amazon  Stone,  Amazonite),  318 
Albite  (Moonstone),  320 
Labradorite  (Labrador  Spar),  321 
Pyroxene,  304 
Hypersthene,  304 
Diopside,  305 

Spodumene  (Hiddenite,  Kunzite),  308 
Rhodonite,  309 

(Sphenc) 
(Californite) 
(Lapis  Lazidi) 
(Precious  Serpentine) 


(Malachite  Matrix,  A  zur malachite) 


(Satin  Spar) 


Titanite,  323 
Vesuvianite,  288 
Lazurite,  303 
Serpentine,  297 
Epidote,  286 
Malachite  and 
Azurite,  252 
Chrysocolla,  293 
Cyanite,  282 
Datolite,  283 
Staurolite,  279 
Andalusite,  281 
Gypsum,  264 
Pyrite,  208 
Hematite,  230 

Popular  Names  of  Gems. — Many  of  the  names  applied  to  gem  minerals 
are  of  very  ancient  origin  and,  hence,  were  in  use  long  before  mineralogy 
was  developed  as  a  science.  Considerable  ambiguity  has,  therefore, 
arisen  by  the  simultaneous  use  of  popular  terms  by  jewelers  and  of 
scientific  names  by  mineralogists.  Indeed,  many  of  the  popular  terms 
are  intentionally  misleading.  Thus,  yellow  quartz  or  citrine  is  commonly 
called  in  the  trade  Spanish,  brazilian,  or  oriental  lopaz.  Popular  names 
have  frequently  been  based  upon  color  and,  hence,  it  is  not  surprising 
to  find  the  term  ruby  incorporated  in  several  of  the  popular  names  given 
to  gem  stones  of  a  red  color:  ruby  spinel,  balas  ruby,  and  rubicelle  for 


332 


MINERALOGY 


red  spinel;  cape  ruby  and  Arizona  ruby  for  pyrope  garnet;  and  rubellite 
for  red  tourmaline.  Popular  names  of  this  character  suggest  relations 
with  more  valuable  stones  which  are  not  warranted  by  the  facts.  Ob- 
viously, all  ambiguity  and  misconceptions  would  be  avoided  if  only  the 
scientific  names  of  the  mineralogist  were  used. 


Photo  by  the  Champlain  Studios,  Inc.,  New  York  City. 

FIG.  678. — George  F.  Kunz  (1856 ).     New  York  City.     Author  of  many  publications 

on  gems  and  precious  stones. 

Methods  of  Identification.' — Rough  and  uncut  gem  stones  can  be 
readily  determined  by  means  of  their  physical  properties  in  the  same 
way  as  other  minerals.  This  usually  involves  the  use  of  a  set  of  mineral 
tables,  such  as  are  found  on  pages  380  to  547.  When  the  stones  are 
cut  and  polished,  the  properties  generally  used  for  determination  are 


FIG.  679. 

color,  index  of  refraction,*  dispersion,  fracture  or  cleavage  as  revealed 
around  the  prongs  of  the  setting,  inclusions,  and  dichroism.  If  it  is  nec- 
essary to  determine  the  hardness  of  a  gem,  great  care  should  be  exercised 
not  to  injure  a  soft  but  otherwise  perfectly  good  stone.  When  stones  are 

*  This  determination  can  be  easily  and  quickly  made  by  using  Smith's  hand  total 
ref  ractometer  (Fig.  679), 


GEMS  AND  PRECIOUS  STONES  333 

unmounted,  a  determination  of  the  specific  gravity  can  often  be  made  the 
basis  of  an  accurate  recognition  of  the  gem  under  consideration. 

Weight. — Gems  are  usually  sold  by  weight,  which  is  expressed  in  carats. 
This  standard  of  weight  was  until  very  recently  a  variable  quantity, 
having  originally  been  determined  by  the  weight  of  certain  grains  or 
leguminous  seeds.  Thus,  the  carat  used  in  various  gem  centers  differed 
considerably  when  expressed  in  terms  of  the  metric  system  of  weights. 
This  is  clearly  shown  by  the  values  of  the  carats  formerly  in  use  in  the 
following  cities: — Florence,  0.1972  grams;  London,  0.2053;  Madrid, 
0.20539;  Amsterdam,  0.2057;  Frankfurt  am  Main,  0.20577;  Vienna, 
0.20613.  In  1913  the  metric  carat,  which  equals  0.200  grams,  was  made 
the  standard  in  the  United  States.  This  unit  has  also  been  adopted  in 
practically  all  the  large  countries  of  the  world. 


FIG.  680.  FIG.  681. 

Cutting  of  Gems. — Although  gem  minerals  are  frequently  found  in 
nature  in  beautiful  and  well-developed  crystals,  they  are  rarely  adapted 
for  use  as  gems  without  suitable  cutting  and  polishing.  While  crystals 
may  show  excellent  reflections,  the  full  optical  splendor  of  such  gem  min- 
erals is  best  brought  out  by  cutting  or  grinding  the  specimen  into  symme- 
trical shapes,  which  will  allow  the  stone  to  appear  as  brilliant  as  possible, 
show  its  best  color,  and  exhibit  the  maximum  amount  of  fire.  This  pro- 
cess of  cutting  involving  the  production  of  artificial  faces  or  facets, 
as  these  plain  surfaces  are  called,  is  of  comparatively  ecent  origin. 


FIG.  682.  FIG.  683.  FIG.  684. 

Louis  de  Berquem  is  credited  with  having  discovered  this  process  about 
1456. 

The  ancients  contented  themselves  with  simply  polishing  the  natural 
crystal  faces,  or  they  ground  the  stone  into  certain  rounded  shapes.  The 
cabochon  cuts  are,  hence,  the  oldest  of  the  various  styles  of  cutting  still 
in  common  use.  The  following  types  may  be  differentiated : 

(1)  Double  or  convex  cabochon. — This  involves  generally  circular,  ellip- 
tical, or  oval  forms  with  two  convex  surfaces,  the  upper  side  being  more 
convex  than  the  lower  (Fig.  680) .     When  the  convexity  is  the  same  above 
and  below,  the  cut  is  sometimes  called  lentil  shape  (Fig.  681). 

(2)  High  cabochon. — This  is  somewhat  similar  to  (1),  but  the  upper 


334 


MINERALOGY 


portion  is  very  much  higher  and,  hence,  more  convex  than  the  under 
side  (Fig    682). 

(3)  Simple  or  plain  cabochon. — In  this  cut  the  upper  side  is  convex 
as  in  (1)  and  (2),  but  the  under  side  is  a  plain  surface.     Stones  with  this 
style  of  cutting  are  mounted  with  the  plain  surface  down  (Fig.  683). 

(4)  Hollow   or   concavo-convexo   cabochon,    also   called   shell   cut.     In 
this  style  the  upper  side  is  convex,  but  the  under  portion  is  hollowed  out 
(Fig.  684). 


FIG.  685. — Diamond  cleaver  at  work.* 

The  cabochon  cuts  are  used  for  stones  exhibiting  sheens,  play  of  colors, 
opalescence,  and  asterism ;  thus,  for  tiger's  eye,  opal,  moonstone,  and  star 
sapphires.  They  are  also  used  for  many  colored  stones,  for  example, 
garnet,  amethyst,  turquois,  and  chrysocolla.  The  hollow  cabochon  cut 
is  generally  employed  for  transparent  but  deeply  colored  stones  through 
which  very  little  light  could  pass  if  cut  in  the  other  styles;  for  example, 
the  almandite  variety  of  garnet. 

*  Figs.  685,  693  and  694  are  views  taken  in  the  Diamond  Cutting  Works  of  Messrs. 
Stern  Brothers  and  Company,  New  York. 


GEMS  AND  PRECIOUS  STONES 


335 


The  principal  style  of  cutting  involving  facets  is  the  brilliant  cut.  In 
this  cut  the  octahedron,  either  natural  or  produced  by  cleavage,  is  made 
the  basis,  as  is  shown  in  Figs.  685  and  686.  The  upper  and  lower  por- 
tions are  removed  in  such  a  manner  that  when  the  stone  is  cut,  the  portion 
above  the  edge  G,  which  is  termed  the  girdle,  is  generally  one-half  as 
thick  as  the  part  below  the  girdle.  The  upper  portion  of  the  cut  stone  is 


FIG.  686. 


FIG.  688. 


called  the  crown  or  bizet,  while  the  lower  part  is  the  pavilion  or  base. 
The  uppermost  facet  T  is  the  table,  and  C  is  the  culet  (Figs.  687  and  688) . 
Commonly  there  are  fifty-six  facets  between  the  table  and  the  culet.  In 
some  cases,  however,  diamonds  are  cut  in  this  style  with  as  many  as  sixty- 
six  or  seventy-four  facets,  inclusive  of  the  table  and  the  culet.  Definite 


//r\/N\ 


FIG.  689. 


FIG.  690. 


relations  between  the  height  of  the  crown,  depth  of  the  pavilion,  and 
width  of  the  stone  must  be  observed  if  the  cut  gem  is  to  exhibit  the 
maximum  of  brilliancy  and  fire.  Depending  upon  the  character  of  the 
rough  material,  the  outline  of  the  cut  stone  varies,  being  either  circular, 
quadratic,  oval,  elliptical,  or  pear-shaped.  The  diamond  is  cut  almost 
exclusively  in  this  style. 


FIG.  691. 


FIG.  692. 


The  rose  cut  has  twenty-four  triangular  facets  with  a  flat  base  (Figs. 
689  and  690).  This  style  of  cutting  is  one  of  the  earliest  involving 
facets  but  is  not  employed  much  at  present.  Figures  691  and  692 
illustrate  step,  trap,  or  cushion  cuts,  which  are  frequently  used  for 
colored  stones. 

In  cutting  gems,  the  stone  is  held  in  some  cement  and  placed  against 


336 


MINERALOGY 


a  rapidly  revolving  metallic  wheel  or  disk  containing  or  covered  with  some 
abrasive,  such  as  diamond  dust,  carborundum,  or  emery.  The  position 
and  inclination  of  the  various  facets  are  determined  by  the  eye  of  the 


FIG.  693. — Diamond  cutters. 


cutter,  who  obviously  must  exercise  great  judgment  in  order  to  cut 
stones  to  the  best  advantage.  These  cutters  become  very  expert  and 
rarely  does  an  experienced  cutter  exceed  the  permissible  limits  of  varia- 


FIG.  694. — Diamond  polisher. 

tion  in  the  angles  between  the  different  facets.  After  the  facets  have 
been  produced,  they  are  polished  in  much  the  same  manner  as  they  were 
cut,  except  that  some  polishing  material  like  tripolite  or  rouge,  instead 


GEMS  AND  PRECIOUS  STONES 


of  an  abrasive,  is  used.  Diamonds  are  usually  cut  and  polished  by  men 
who  specialize  on  the  diamond,  while  a  lapidary  is  one  who  cuts  and 
polishes  all  other  types  of  gems.  Antwerp,  Amsterdam,  Paris,  London, 
Hanau,  Idar,  New  York,  and  Boston  are  important  gem  cutting  centers. 

Synthetic  Gems. — A  synthetic  gem  is  one  prepared  in  the  laboratory, 
and  in  its  chemical  and  physical  properties  is  identical  with  the  corre- 
sponding natural  gem.     For  many  years  scientists  have  endeavored  to 
produce  the  diamond  in  the  laboratory.     Promi- 
nent among  the   many  investigators  who  have 
worked  on  this  problem,  are  Moissan,  and  Noble 
and  Crookes,  who  succeeded  in  obtaining  small 
diamonds  of  microscopic  ^sizes.     All  attempts  to 
obtain  synthetic  diamonds  of  such  sizes  as  to  be 
of  commercial  importance  have  thus  far  resulted 
in  failure. 

The  most  important  synthetic  gems  are  those 
having  the  composition  and  physical  properties 
of  the  various  varieties  of  corundum;  that  is, 
synthetic  rubies  and  sapphires.  At  present  these 
are  manufactured  on  a  large  scale,  and  they  differ 
from  the  natural  stones  only  in  minor  details.  In 
fact,  in  many  instances  the  cut  synthetics  exhibit 
greater  splendor  and .  are  usually  much  cleaner 
than  natural  stones. 

The  apparatus  for  producing  these  synthetic 
rubies  and  sapphires  was  devised  by  Verneuli 
(Fig.  695).  It  consists  of  a  vertical  blowpipe, 
burning  a  mixture  of  illuminating  gas  and  oxygen, 
which  enter  at  G  and  O,  respectively.  By  means 
of  suitable  mechanism,  very  finely  divided  par- 
ticles of  aluminum  oxide,  Al2Os,  are  introduced 
at  M.  These  particles  mix  with  the  gases  and 

fuse  in  the  very  hot  flame  at  F,  which  is  directed  against  a  small  fire 
clay  support  C.  These  fused  particles  collect  on  this  clay  support  at 
first  as  a  small  drop,  which  slowly  increases  in  size,  as  the  process  con- 
tinues, until  a  fairly  large  and  inverted  conical  or  pear-shaped,  color- 
less drop,  called  the  boule  is  formed  (Fig.  696).  These  boules  are 
broad  on  top  and  very  narrow  below  where  supported  on  the  fire-clay 
cone.  They  usually  weigh  from  25  to  30  carats.  Although  the  internal 
structure  of  such  boules  is  the  same  as  that  of  the  natural  colorless  corun- 
dum or  white  sapphire,  the  only  indication  of  crystal  faces  usually  to  be 
observed  is  a  slight  flattening  of  one  of  the  upright  sides.  This  flattened 
surface  corresponds  in  position  to  the  basal  pinacoid  in  the  natural 
gem. 


FIG.  695. 


338 


MINERALOGY 


By  the  addition  to  the  A12O3  of  a  small  amount  of  chromium  oxide, 
boules  of  a  red  color  are  obtained.  These  correspond  to  the  ruby.  The 
addition  of  the  oxide  of  titanium  gives  the  deep  blue  color  of  the 
sapphire  proper.  The  yellow  color  of  the  beautiful  golden  sapphire 
is  produced  when  some  nickel  compound  and  other 
substances,  at  present  kept  secret,  are  added.  In 
chemical  composition  and  all  physical  properties, 
such  as  hardness,  specific  gravity,  indices  of  re- 
fraction, and  so  forth,  these  synthetic  gems  are 
identical  with  those  occurring  in  nature.  Due  to 
the  presence  of  inclusions,  tension  cracks,  and 
peculiar  structure  lines,  cut  synthetic  gems  can  in 
most  instances  be  easily  distinguished  from  natural 
stones.  In  some  cases,  however,  especially  if  the 
cut  stones  are  about  one-half  carat  or  less  in  size, 
their  synthetic  character  may  be  very  difficult  to 
determine. 

Cut  synthetic  rubies  and  sapphires  can  be  obtained  at  prices  ranging 
from  $1.00  to  10.00  per  carat,  depending  upon  the  quality  of  the  stone. 
These  prices  are  about  one-twentieth  of  those  charged  for  natural  gems 
of  the  same  grade.  Not  all  of  these  synthetics  are  sold  as  gems.  A  large 
percentage  is  used  as  jewels  in  the  manufacture  of  watches  and  in  delicate 
physical  and  electrical  instruments,  where  hard  bearing  surfaces  are 
required. 


FIG.  696. 


CHAPTER  XVI 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS 

It  is  often  desirable  to  refer  to  the  more  important  minerals  in  which 
elements  of  economic  importance  occur,  and  the  following  tabulations 
have  been  prepared  to  meet  this  need.  Following  each  table  there  is  a 
discussion  of  the  uses  of  the  important  commercial  minerals  under  con- 
sideration and  whenever  possible  statistics  of  production  are  given. 
The  minerals  are  given  under  each  element  in  the  order  in  which  they 
have  been  described  in  the  text.  Page  references  to  the  detailed  descrip- 
tions are  given  after  the  names  of  the  minerals. 


ALUMINUM 


CORUNDUM,  228 
BAUXITE,  235 
CRYOLITE,  240 
ALUNITE,  262 
SPINELS,  267 
Chrysoberyl,  271 
Wavellite,  276 
Turquois,  276 
STAUROLITE,  279 
ANDALUSITE,  281 
Sillimanite,  282 
CYANITE,  282 
TOPAZ,  283 
TOURMALINE,  284 
EPIDOTE,  286 
VESUVIANITE,  288 
GARNETS,  290 
MICAS,  294 
CHLORITES,  297 
KAOLINITE,  301 
NEPHELITE,  301 
Sodalite,  303 
SPODUMENE,  308 
AMPHIBOLES,  309 

LEUCITE,  313 

BERYL,  313 
FELDSPARS,  315 

ZEOLITES,  324 
SCAPOLITE,  322 


Hexagonal 

Unknown 

Monoclinic 

Hexagonal 

Cubic 

Orthorhombic 

Orthorhombic 

Triclinic 

Orthorhombic 

Orthorhombic 

Orthorhombic 

Triclinic 

Orthorhombic 

Hexagonal 

Monoclinic 

Tetragonal 

Cubic 

Monoclinic 

Monoclinic 

Monoclinic 

Hexagonal 

Cubic 

Monoclinic 

Orthorhombic  and 

Monoclinic 

Orthorhombic  and 

Cubic 
Hexagonal 
Monoclinic  and 

Triclinic 
Various  systems 
Tetragonal 

339 


A1203 

A12O(OH)4 

Na3AlF6 

K2(A1.2OH)6(SO4)4 

Mg(AlO2)2,  etc. 

Be(A102)2 

(A1.0H)3(P04)2.5H20 

H6[Al(OH)2]6Cu(OH)(P04)4 

HFeAl5Si2O13 

Al2SiO5 

Al2Si05 

Al2SiO6 

Al2(F,OH)2SiO4 

H20B2Si4O2i 

Ca2(Al,Fe)2(Al.OH)(SiO4), 

Ca6[Al(OH,F)]Al2(Si04)6 

R'3Al2(Si04)3 

H2KAl(SiO4)3,  etc. 

H4Mg2Al2Si09 

H4Al2Si2O9 

(Na,K)8Al8Si9034 

Na4Al2(Al.Cl)(SiO4)3 

LiAl(SiO3)2 

Silicates  of  Al,Ca,Mg,Fe 

K2Al2Si4012 

Be3Al2Si6O18 
KAlSi3O8,  etc. 

Hydrated  silicates 
Ca4Al6SifiO25,  etc. 


340  MINERALOGY 

Aluminum  is  the  most  abundant  metal  in  nature  and  the  minerals  in 
which  this  element  is  an  important  constituent  are  exceedingly  numerous. 
Only  bauxite,  cryolite,  and  alunite  serve  as  sources  of  aluminum  or  its 
compounds.  Bauxite  is  used  as  a  source  of  metallic  aluminum  and 
aluminum  salts,  and  also  in  the  manufacture  of  bauxite  bricks  and  abra- 
sives, such  as  alundum,  aloxite,  exolon,  and  lionite.  These  products  are 
made  by  fusing  bauxite  in  an  electric  furnace.  -The  total  production  of 
artificial  abrasives  made  from  bauxite  in  1917  was  48,460  short  tons. 
Cryolite  is  used  as  the  flux  in  the  electrolytic  method  for  the  extraction 
of  the  metal  from  bauxite,  while  alunite  furnishes  a  small  amount  of 
potassium  salts,  together  with  alumina  as  a  by-product. 

In  the  extraction  of  aluminum,  the  crude  ore  (bauxite)  is  fused  with 
sodium  carbonate,  and  the  fusion  leached  with  water.  Upon  passing 
carbon  dioxide  through  the  filtrate,  the  hydroxide  of  aluminum  is  preci- 
pitated which  is  then  ignited  to  the  oxide.  Another  method,  sometimes 
employed  to  remove  most  of  the  impurities  from  the  ore,  consists  of 
fusing  the  bauxite  in  an  electric  furnace  with  sufficient  carbon  to  reduce 
silica,  titanic  oxide,  and  ferric  oxide.  The  alumina  is  not  affected. 
In  the  electrolysis,  cryolite  is  placed  in  tanks  lined  with  carbon  which 
acts  as  the  cathode,  while  suspended  carbon  cylinders  serve  as  the  anode. 
The  cryolite  melts  and  readily  dissolves  the  alumina  which  is  added. 
The  current  decomposes  the  latter  with  the  separation  of  metallic 
aluminum  which  collects  in  the  bottom  of  the  tank.  The  value  of  pri- 
mary metallic  aluminum  produced  in  the  United  States  in  1918  was 
$41,159,000. 

Metallic  aluminum  finds  extensive  use  on  account  of  its  low  density, 
toughness,  durability,  and  resistance  to  corrosion.  Many  alloys  of 
aluminum  have  been  prepared.  The  most  important  are  those  with  cop- 
per, zinc,  tin,  nickel,  magnesium,  manganese,  silver,  and  cadmium. 
Thermit,  used  in  welding,  is  a  mixture  of  aluminum  and  iron  oxide,  while 
the  explosive  ammonal  consists  of  aluminum  dust  and  ammonium 
nitrate.  Alum  and  aluminum  sulphate  are  the  chief  chemical  salts  and 
are  employed  in  water  purification,  dyeing,  and  tanning.  Bauxite 
bricks  containing  about  77  per  cent,  alumina  are  used  in  the  construc- 
tion of  copper,  iron,  and  lead  furnaces,  and  of  cement  kilns. 

Bauxite  of  commercial  grade  should  carry  at  least  52  per  cent.  A1203, 
less  than  3  per  cent.  TiC>2,  and  not  more  than  15  per  cent,  of  the  combined 
oxides  of  silicon  and  iron.  The  production  of  bauxite  in  United  States  in 
1918  totaled  605,721  long  tons,  of  which  562,892  tons  were  obtained 
from  Arkansas  (about  90  per  cent.)  and  42,829  tons  from  Georgia, 
Tennessee,  and  Alabama.  In  1918, 20,286  short  tons  of  alum  and  209,079 
short  tons  of  aluminum  sulphate  were  produced.  The  quantity  of  cryolite 
imported  from  Greenland  in  1918  was  1,950  long  tons,  valued  at  $97,500 
or  $50  per  ton. 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     341 

ANTIMONY 

STIBNITE,  204  Orthorhombic  Sb2S3 

Pyrargyrite,  217  Hexagonal  Ag3SbSs 

Bournonite,  217  Orthorhombic  Pb2Cu2Sb2S6 

TETRAHEDRITE,  218  Cubic  M"4Sb2S7 

Of  the  above  named  antimony  minerals  stibn'te  is  the  most  important. 
Some  antimony  is  also  recovered  from  antimonial  lead  ores  carrying  from 
12  to  18  per  cent,  of  antimony.  Antimony  metal  is  used  chiefly  in  the 
manufacture  of  alloys.  These  alloys  include  type  metal  (lead,  antimony, 
and  tin),  babbitt,  antifriction,  or  bearing  metal,  (antimony,  tin,  with  small 
amounts  of  lead,  copper,  bismuth,  zinc,  or  nickel),  britannia  or  white 
metal  (tin,  antimony,  copper,  with  some  zinc),  and  so  forth.  Antimony 
imparts  hardness  to  lead  and  prevents  it  from  contracting  when  solidi- 
fying from  a  molten  condition.  The  tetraoxide  (Sb204)  is  used  in  making 
opaque  white  enamel  and  other  sanitary  ware.  Salts  of  antimony  are 
used  in  medicine  and  as  a  mordant  in  dyeing,  whiLe  the  sulphide  of 
antimony  is  employed  for  vulcanizing  and  coloring  rubber  and  also  as 
paint  pigments. 

Under  normal  conditions  United  States  is  not  a  large  producer  of 
antimony  ores,  importing  practically  its  entire  supply  from  China,  Bolivia 
Mexico,  and  Japan.  In  1918  the  production  of  antimony  ores  in  the 
United  States  was  confined  to  the  Western  States  and  Alaska.  The  total 
reported  was  190  short  tons  containing  50  tons  of  the  metal. 

ARSENIC 

Native  Arsenic,  194  Hexagonal  As 

REALGAR,  203  Monoclinic  AsS 

ORPIMENT,  204  Monoclinic  As2S3 

Niccolite,  208  Hexagonal  NiAs 

Cobaltite,  209  Cubic  CoAsS 

Smaltite,  209  Cubic  CoAs2 

ARSENOPYRITE,  211  Orthor^mbic  FeAsS 

PROUSTITE,  217  Hexagonal  Ag,AsS8 

TETRAHEDRITE,  218  Cubic  M"4As2S7 

Enargite,  219  Orthorhombic  Cu3AsS4 

Arsenopyrite  is  the  most  important  arsenical  mineral.  The  com- 
mercial uses  of  arsenic  are  very  limited.  Shot  metal  is  an  alloy  of  arsenic 
and  lead.  Arsenious  oxide  is  used  in  the  manufacture  of  glass  for  counter- 
acting the  iron  coloration,  and  of  Paris  green,  and  other  insecticides. 
The  minerals  realgar  and  orpiment  are  employed  in  paints  and  in  the 
dyeing  of  cloth. 

The  production  of  arsenic  is  recorded  in  terms  of  white  arsenic,  ar- 
senious  oxide,  As2O3,  very  little  of  which  is  obtained  directly  from  arsenic 
minerals.  Large  quantities  are  however  available  as  a  by-product  in  the 
smelting  of  copper,  cobalt,  gold,  silver,  and  lead  ores.  The  production 
in  1918  was  6,323  short  tons  of  As203,  valued  at  $1,213,000. 


342  MINERALOGY 

BARIUM 

WITHERITE,  251  Orthorhombic  BaCO3 

BARITE,  266  Orthorhombic  BaSO4 

Barite  (barytes)  is  the  more  important  of  the  above  minerals, 
commercially.  It  is  used  chiefly  as  a  pigment  in  mixed  paints.  Litho- 
pone,  one  of  the  chief  constituents  of  sanitary  flat,  wall  paints,  is  a  mixture 
of  70  per  cent,  barium  sulphate,  25  to  29  per  cent,  zinc  sulphide,  and  1  to 
5  per  cent,  zinc  oxide.  Blanc  fixe  or  permanent  white  is  artificially 
prepared  barium  sulphate.  Ground  barite  is  used  in  the  manufacture  of 
rubber  goods,  artificial  ivory,  and  heavy  glazed  paper,  such  as  playing 
cards,  and  bristol  board.  The  barium  salts  have  a  wide  variety  of  uses : 
barium  binoxide  (Ba02)  in  the  preparation  of  hydrogen  peroxide,  barium 
chloride  as  a  water  softener,  the  carbonate  and  chloride  to  prevent 
efflorescence  on  bricks  and  as  insecticides,  and  the  carbonate,  sulphate,  or 
nitrate  in  the  manufacture  of  optical  glass. 

Barite  is  obtained  mainly  from  Georgia,  Missouri,  Tennessee,  and 
Kentucky,  and  in  1918  the  production  totaled  155,241  short  tons  valued 
at  $1,044,337. 

BERYLLIUM 

Chrysoberyl,  271  Orthorhombic  Be(AlO2)2 

BERYL,  313  Hexagonal  Be3Al2(SiO3)6 

Aside  from  the  use  of  beryllium  minerals  as  gems,  the  application  of 
beryllium  compounds  in  the  arts  is  restricted  to  a  small  amount  consumed 
in  the  manufacture  of  incandescent  gas  mantels. 

BISMUTH 
Native  Bismuth,  195  Hexagonal  Bi 

Bismuth  is  extensively  used  in  alloys  with  lead,  tin,  copper,  antimony, 
and  cadmium.  The  melting  point  of  some  of  these  alloys  is  as  low  as 
64°C  and  they  are  therefore  employed  as  safety  fuses  for  electrical 
apparatus,  safety  plugs  for  boilers,  and  for  automatic  sprinklers.  As 
these  alloys  expand  upon  solidifying  from  a  molten  condition  they  are 
employed  in  type  metal.  Bismuth  salts  are  used  in  dressing  wounds. 
The  nitrate  is  sometimes  given  internally  before  producing  a  roentgeno- 
graph,  as  bismuth  salts  are  opaque  to  X-rays.  The  salts  are  also 
used  in  calico  printing  and  in  the  manufacture  of  high  refractive  glass. 

Very  little  native  bismuth  is  mined  in  the  United  States.  Almost  the 
entire  domestic  production  is  obtained  as  a  by-product  in  the  electrolytic 
refining  of  lead,  the  bismuth  being  recovered  from  the  anode  slime. 
This  source  yields  about  200,000  Ibs.  of  the  metal  annually. 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     343 


BORON 


Colemanite,  271 
Datolite,  283 
TOURMALINE,  284 


Monocliiiic 
Monoclinic 
Hexagonal 


Ca2B6Oii.5H2O 
Ca(B.OH)SiO4 
H20B2Si4O2i 


Commercially,  the  most  important  boron  compound  is  borax,  which 
is  obtained  by  treating  colemanite  with  sodium  carbonate  or  sulphate. 
Borax  is  used  in  assaying,  soldering,  welding  of  metals,  and  in  the  manu- 
facture of  flint  glass.  Because  of  its  antiseptic  and  cleansing  properties 
it  is  also  used  in  the  preservation  of  food  and  in  the  manufacture  of  soap, 
washing  powders,  and  ointments.  Chromium  borate  is  a  green  pigment 
employed  in  calico' printing,  and  the  borate  of  manganese  is  sometimes 
used  as  a  drier  in  paints  and  oils. 

The  entire  output  of  crude  borate  (colemanite)  in  United  States  in 
1917  was  obtained  from  a  few  mines  in  southern  and  southeastern  Cali- 
fornia, and  amounted  to  109,944  short  tons,  valued  at  $2,561,958. 

The  production  of  gem  varieties  of  tourmaline  in  1918  was  restricted 
to  California  and  Maine  and  amounted  to  $6,206. 


FLUORITE,  239 
CALCITE,  242 
DOLOMITE,  245 
ARAGONITE,  249 
ANHYDRITE,  254 
Scheelite,  259 
GYPSUM,  264 
Colemanite,  271 
APATITE,  273 
Datolite,  283 
EPIDOTE,  286 
Orthite,  287 
VESUVIANITE,  288 
GARNET,  290 
PYROXENES,  304 

AMPHIBOLES,  309 

Anorthite    and 

PLAGIOCLASES,  319 
SCAPOLITE,  322 
TITANITE,  323 
ZEOLITES,  324 


CALCIUM 

Cubic 

Hexagonal 

Hexagonal 

Orthorhombic 

Orthorhombic 

Tetragonal 

Monoclinic 

Monoclinic 

Hexagonal 

Monoclinic 

Monoclinic 

Monoclinic 

Tetragonal 

Cubic 

Orthorhombic,  Mono- 
clinic,  and  Triclinic 

Orthorhombic,  Mono- 
clinic,  and  Triclinic 

Triclinic 
Tetragonal 
Monoclinic 
Various  systems 


CaF2 
CaCO, 

CaMg(C03)2 

CaCO3 

CaSO4 

CaWO4 

GaS04.2H2Q 

Ca2B6Oii.5H2O 

Ca5F(P04)3 

Ca(B.OH)SiO4 

Ca2(Al,Fe)2(Al.OH)(SiO4)3 

Ca2(Al,Ce,Fe)2(Al.OH)(SiO4)3 

Ca6[Al(OH,F)]Al2(SiO4)6 

Ca3Al2(SiO4)3r  etc. 

CaMg(SiO3)2,  etc. 

CaMg,(SiO,)4,  etc. 


CaAl2Si2O8,  etc. 
Ca4Al6Si6O25,  etc. 
CaTiSiOe 
Hydrated  silicates 


Calcium  is  one  of  the  most  abundant  metals  in  nature  and  is  an  im- 
portant constituent  of  many  minerals.  Of  those  listed  above,  fluor'te, 
calcite,  dolomite,  scheelite,  gypsum,  colemanite,  and  apatite  are  of  prime 
importance  commercially.  However,  the  production  and  uses  of  calcite, 
dolomite,  and  gypsum  only  will  be  given  here. 


344 


MINERALOGY 


Calcite  and  Dolomite. — 'The  value  of  limestone,  massive  forms  of 
calcite  and  dolomite,  sold  in  United  States  in  1917  was  $46,263,379,  or 
56.3  per  cent,  of  the  total  value  of  all  stone  sold  in  that  year,  while  the 
value  of  marble  was  placed  at  $6,330,387.  The  distribution  of  this  pro- 
duction is  shown  summarized  below : 


Building 

Monu- 
mental 

Pav- 
ing 

Curb- 
ing 

Flag- 
ging 

Rubble 

Riprap 

Crushed 

Other 
uses 

Limestone 
Marble 

$4,115,366 
$3,702,563 

$7,273 

51,927 

$8,327 

$270,327 

$854,884 

$17,541,098 

$23,414,132 
$230,107 

$2,397,717 

Under  other  uses,  in  the  case  of  limestone,  are  included  furnace  flux 
valued  at  $18,679,213,  stone  for  alkali  works  and  sugar  factories,  valued 
at  $2,084,036,  and  ground  stone  for  agricultural  purposes,  valued  at 
$1,352,397.  Furnace  flux,  terrazzo,  and  marble  dust  are  included  under 
other  uses  of  marble.  In  addition,  large  quantities  of  limestone  are 
employed  in  the  manufacture  of  cement  and  lime.  It  is  estimated  that 
in  1917  these  industries  used  the  following  quantities  of  limestone. 


Portand  cement 
Natural  cement 
Lime  . 


24,640,230  short  tons 

102,260  short  tons 

7,194,000  short  tons 


The  leading  limestone  producing  States,^  according  to  rank,  in  1917  were 
Pennsylvania,  Ohio,  Indiana,  New  York,  Michigan,  and  Illinois,  each  with 
a  production  of  more  than  $3,000,000. 

Gypsum. — This  mineral  is  used  in  both  the  uncalcined  and  calcined 
condition.  In  the  former  state  its  chief  uses  are  (1)  as  a  retarder  in 
Portland  cement,  (2)  as  a  pigment  base  for  paints,  especially  in  making 
cold  water  paints,  (3)  as  a  filler  for  paper  and  cloth,  and  (4)  as  land  plaster 
or  fertilizer.  The  action  of  gypsum  as  a  fertilizer  is  indirect,  decomposing 
complex  silicates  of  magnesia  and  potash,  thus  liberating  these  compounds 
for  plant  food.  Ground  gypsum  neutralizes  acid  soils  and,  because  of  its 
ability  to  absorb  moisture  from  the  atmosphere,  promotes  the  growth 
of  grain  especially  in  the  early  stages  by  keeping  the  moisture  near  the 
surface. 

Calcined  gypsum  is  used  chiefly  in  wall  plasters,  plaster  boards,  gyp- 
sum blocks  and  tile,  molds  for  pottery  and  terra  cotta,  surgical  casts,  and 
for  many  other  purposes.  Gypsum  tile  3  in.  thick  and  30  in.  long,  rein- 
forced with  metal  is  frequently  used  for  roof  decks  of  laundries,  foundries, 
and  textile  mills  where  condensation  of  moisture  causes  considerable 
trouble.  As  gypsum  has  a  low  heat  conductivity  its  use  largely  prevents 
this  condensation  or  drip.  Keene's  cement,  which  differs  from  ordinary 
wall  plasters  in  the  time  of  setting  and  its  greater  hardness,  is  made  by 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     345 

burning  pure  gypsum  at  a  low  temperature,  then  immersing  in  a  solution 
of  alum,  aluminum  sulphate,  or  borax  and  recalcining  at  about  500°C. 

Gypsum  is  produced  in  eighteen  states  and  Alaska.  New  York  is 
the  largest  producer,  Iowa  second,  and  Michigan  third.  Almost  inex- 
haustible deposits  are  to  be  found  west  of  the  Mississippi  River.  In  the 
single  state  of  Wyoming  beds  from  six  to  twenty  feet  in  thickness  are 
exposed  for  a  thousand  miles.  The  production  in  United  States  in  1918 
was  2,057,015  short  tons,  distributed  according  to  uses  as  follows: 

Uncalcined 

Portland  cement 403,587  short  tons 

Land  plaster 64,571  short  tons 

Other  purposes 1,986  short  tons 

Calcined 

Plaster  Paris,  wall  plasters,  etc 1,174,359  short  tons 

Glass  factories 13,567  short  tons 

As  boards,  tile,  blocks,  etc 140,343  short  tons 

CARBON 

DIAMOND,  188  Cubic  C 

GRAPHITE,  192  Hexagonal  C 

Carbon  is  also  an  essential  constituent  of  the  carbonates,  pages  241 
and  253  and  organic  substances  as  petroleum,  asphalt,  and  coal. 

Diamond. — Several  hundred  carats  of  diamonds  were  reported  from 
Pike  County,  Arkansas  in  1918,  including  a  yellow  colored  octahedron 
weighing  17.85  carats,  a  flat,  clear  stone  of  11  carats,  and  a  number  of 
smaller  stones  weighing  several  carats  each.  It  is  estimated  that  at  least 
4,000  stones  were  found  in  the  Arkansas  diamond  district  up  to  July  1, 
1916.  The  values  of  other  scattered  finds  rarely  exceed  a  few  thousand 
dollars  annually. 

Graphite. — The  trade  makes  a  sharp  distinction  between  crystalline 
and  amorphous  graphite.  By  the  former  is  meant  flake  graphite  of 
sufficient  size  to  be  visible  to  the  naked  eye.  By  far  the  most  important 
use  of  graphite  is  in  the  manufacture  of  crucibles  used  in  the  steel,  brass, 
and  bronze  industries.  For  this  purpose  a  flaky  or  fibrous  graphite 
is  essential  and  the  Ceylon  lump  is  generally  preferred,  although  it  is 
sometimes  mixed  with  10  to  25  per  cent,  of  American  flake  graphite. 
For  crucibles  graphitic  carbon  should  exceed  85  per  cent,  and  at  the 
same  time  be  practically  free  from  mica,  pyrite,  and  iron  oxide.  Graphite 
crucibles  are  superior  to  clay  crucibles  because  of  their  infusibility,  con- 
ductivity of  heat,  and  ability  to  withstand  sudden  temperature  changes. 
As  graphite  has  but  little  binding  strength,  clay,  sand,  and  kaolin  are 
added  in  the  proportion  of  about  3  parts  of  graphite,  2  parts  of  clay,  1 
part  of  sand,  and  smaller  amounts  of  kaolin. 


346  MINERALOGY 

Except  for  the  manufacture  of  crucibles,  amorphous  graphite  is 
suitable  for  all  other  purposes.  For  paint  and  foundry  facings  a  high 
degree  of  purity  is  not  demanded,  but  for  lubricants,  pencils,  and  electric 
purposes  high  grade  material  is  essential.  In  the  manufacture  of  self- 
lubricating  metals,  molten  metal  is  forced  into  graphite  and  the  resuliing 
mixture  contains  about  60  per  cent,  by  weight  or  25  per  cent,  by  volume 
of  the  metal. 

Imported  crystalline  graphite  is  obtained  chiefly  from  Ceylon  and 
Madagascar,  while  Alabama,  New  York,  and  Pennsylvania  are  the  prin- 
cipal domestic  sources.  The  better  grades  of  amorphous  graphite  are 
imported  from  Mexico  and  Chosen  (Korea) .  The  production  and  impor- 
tation in  1918  is  shown  below. 

Domestic  Production 

Crystalline 6,431  short  tons 

Amorphous 6,560  short  tons 


Total 12,991  short  tons 

Graphite  imported  in  1918  totaled  19,498  short  tons. 

CERIUM 

Monazite,  272     Monoclinic  (Ce,La,Di)PO4 

Orthite,  287        Monoclinic  Ca2(Al,Ce,Fe)2(Al.OH)(SiO4)3 

When  struck  or  scratched  alloys  of  cerium  readily  emit  sparks  and 
this  property  is  utilized  in  many  forms  of  automatic  lighters.  Because 
of  the  great  affinity  of  cerium  for  oxygen  it  is  also  used  as  a  reducing 
agent  in  the  production  of  metallic  zirconium  and  thorium.  Cerium 
sulphate  is  employed  in  the  manufacture  of  aniline  black,  in  photography 
for  the  purpose  of  removing  silver  from  over-developed  negatives,  and  as 
a  catalyst  in  the  contact  process  for  the  manufacture  of  sulphuric  acid. 
Recently  cerium  compounds  have  been  proposed  for  use  in  color  photog- 
raphy and  arc  lamp  electrodes.  The  oxide,  ceria,  is  employed  very 
extensively  as  a  constituent  of  incandescent  mantles. 

CHROMIUM 

Crocoite,  268  Monoclinic  PbCrO4 

CHROMITE,  270  Cubic  (Fe,Cr)[(Cr,Fe)O2]2 

Chromite  is  by  far  the  more  important.  When  added  in  small  amounts 
(1  to  2  per  cent.)  to  steel,  chromium  increases  its  hardness.  Chrome  steel 
is  used  in  the  manufacture  of  armor  plate,  armor  piercing  projectiles, 
and  for  high  speed  tools.  Chromite  is  often  employed  to  line  copper  and 
steel  furnaces.  For  this  purpose  it  has  certain  advantages  over  mag- 
nesite,  as  it  resists  corrosion,  withstands  sudden  changes  of  tempera- 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     347 

ture,  and  requires  less  delicate  handling.  Compounds  of  chromium  are 
used  as  pigments,  mordants  in  dyeing  and  printing  cloth,  and  in  tanning 
leather. 

The  chief  foreign  sources  of  chromite  in  recent  years  have  been  Rhode- 
sia, New  Caledonia,  and  Canada.  In  1918,  100,224  long  tons  were  im- 
ported. The  domestic  production  the  same  year  was  82,350  long  tons, 
mainly  from  California  and  Oregon. 


COBALT 


Cobaltite,  210 
Smaltite,  210 


Cubic 
Cubic 


CoAsS 
CoAs2 


The  metal  cobalt  is  used  to  some  extent  in  the  manufacture  of  high 
speed  tool  steels  and  stellite,  which  is  an  alloy  of  cobalt,  chromium,  and 
tungsten.  Cobalt  increases  the  strength  and  elasticity  of  steel  but  lowers 
its  ductility.  Cobalt  oxide  is  used  as  a  blue  pigment  in  the  manufacture 
of  glass  and  pottery. 

Cobalt  ores  were  mined  only  in  Idaho  in  1918.  The  principal  source 
is  Canada  where  the  oxide  is  recovered  as  a  by-product  in  the  treatment 
of  silver  ores.  The  amount  of  cobalt  ore  and  oxide  imported  in  1918 
was  253,471  Ibs. 

COPPER 


NATIVE  COPPER,  196 
CHALCOCITE,  214 
BORN1TE,  216 

CHALCOPYRITE,  215 
Bournonite,  217 
TETRAHEDRITE,  218 
Enargite,  219 
CUPRITE,  232 
MALACHITE,  252 
AZURITE,  252 
Brochantite,  263 
CHRYSOCOLLA,  293 


Cubic 

Orthorhombic 

Cubic 

Tetragonal 

Orthorhombic 

Cubic 

Orthorhombic 

Cubic 

Monoclinic 

Monoctinic 

Orthorhombic 

Amorphous 


Cu 

Cu2S 

CuxFe2Sx 

2+3 

CuFeS2 

Pb2Cu2Sb2S« 

M"4R'"2S7 

Cu3AsS4 

Cu2O 

CuC03.Cu(OH)2 

2CuC03.Cu(OH)2 

CuSO4.3Cu(OH)2 

CuO,S02,H20 


Copper  is  used  most  extensively  for  the  transmission  of  electricity, 
and  in  castings  and  alloys.  Brass  consists  of  copper  and  zinc;  bronze 
and  bell  metal  of  copper,  tin,  and  zinc ;  and  German  silver  of  copper,  zinc, 
and  nickel.  The  hydrous  copper  sulphate,  or  blue  vitriol,  is  used  in 
calico  printing. 

Twenty-four  states  and  territories  produced  copper  in  1917,  with 
Arizona,  Montana,  Michigan,  and  Utah  as  the  leading  producers.  These 
four  States  contributed  about  80  per  cent,  of  the  total  output.  The 
copper  produced  in  this  country  is  usually  reported  as  blister  copper.  The 
following  table  shows  the  production  (smelter  returns),  percentage  of 


348 


MINERALOGY 


total,  copper  content  of  the  crude  ore  mined,  and  the  value  of  gold  and 
silver  per  ton  recovered  as  by-products,  in  the  four  leading  copper  pro- 
ducing States.* 


Production  in 
pounds  (1916) 

Per  cent, 
of  total 

Per  cent, 
of  Cu  in  ore 

Value  in  gold 
and  silver 
per  ton 

Arizona  

694,847,307 

36.04  ' 

2.18 

.$0.25 

Montana  
Michigan                

352,139,768 
269,794,531 

18.27 
13.99 

2.76 
1.08 

1.32 
0.228 

Utah 

232,335,950 

12  05 

0  90 

0.32 

80.35 

The  total  output  of  this  country  during  1916  was  963,925  metric  tons. 
Approximately  the  same  amount  of  copper  was  produced  in  1917  and 
1918  as  in  1916. 

FLUORINE 


FLUORITE,  239 
CRYOLITE,  240 
APATITE,  273 
TOPAZ,  283 
Chondrodite,  286 
VESUVIANITE,  288 
Lepidolite,  297 


Cubic 

Monoclinic 

Hexagonal 

Orthorhombic 

Monoclinic 

Tetragonal 

Monoclinic 


CaF2 

Na3AlF6 

Ca5F(P04)3 

Al2(F,OH)2Si04 

[Mg(F,OH)]2Mg3(Si04)2 

Ca6[Al(OH,F)]Al2(SiO4)6 

(Li,K)2(F,OH)2Al2Si3O9 


Fluorite. — About  80  per  cent,  of  the  domestic  fluorite  is  consumed 
in  the  manufacture  of  basic  open-hearth  steel,  as  it  gives  fluidity  to 
the  slag  and  aids  in  the  removal  of  phosphorus  and  sulphur.  Other 
uses  are  as  a  flux  in  blast  furnaces,  iron  foundries,  silver,  copper,  and  lead 
smelters,  and  in  the  manufacture  of  glass  and  enamel  ware,  and  of  hydro- 
fluoric acid.  Because  of  its  low  refractive  and  dispersive  powers  fluorite 
is  in  demand  for  apochromatic  lenses,  used  in  telescopes  and  spectroscopes. 
Material  suitable  for  this  work  must  be  glass  clear  and  free  from  clouds, 
gas  bubbles,  strains,  and  fractures.  When  fluorite  is  fused  with  bauxite 
and  soda  ash  an  artificial  cryolite  is  produced. 

In  1918  the  production,  which  amounted  to  263,817  short  tons,  was 
obtained  principally  from  the  five  States,  Illinois,  Kentucky,  Colorado, 
New  Mexico,  and  Arizona;  the  first  two  being  the  chief  producers,  fur- 
nishing over  80  per  cent,  of  the  total  output. 


NATIVE  GOLD,  200 


GOLD 

Cubic 


Au 


Approximately  90  per  cent,  of  the  total  domestic  production  of  gold 
is  obtained  from  placers  and  dry  or  silicious  ores.     The  remaining  10  per 
*According  to  the  United  States  Geological  Survey. 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     349 


cent,  is  recovered  from  copper,  lead,  and  zinc  ores.  The  five  leading 
States  which  in  1917  produced  about  78  per  cent,  of  the  total  output  were : 

California $20,929,400 

Colorado 15,974,500 

Alaska 14,671,400 

South  Dakota f 7,372,900 

Nevada 6,932,500 

The  total  production  in  United  States  in  1917  was  4,051,440  fine  ounces, 
valued  at  $83,750,750.  The  world's  production  the  same  year  totaled 
$423,590,200.  The  more  impotrant  producing  countries  were: 


Africa 

United  States 

Australasia 

Russia  and  Finland 

Canada 


$214,614,000 
83,750,700 
35,945,500 
18,000,000 
15,200?000 


The  domestic  production  in  1918  was  somewhat  less  than  that  in- 
dicated for  1917. 


PYRRHOTITE,  207 
PYRITE,  208 
MARCASITE,  211 
ARSENOPYRITE,  211 
BORNITE,  216 

CHALCOPYRITE,  215 
TETRAHEDRITE,  218 
HEMATITE,  230 
LIMONITE,  235 
SIDERITE,  248 
WOLFRAMITE,  261 
Ferberite,  261 
Melanterite,  266 
SPINELS,  267 
FRANKLINITE,  270 
CHROMITE,  270 
MAGNETITE,  268 
COLUMBITE,  273 
STAUROLITE,  279 
EPIDOTE,  286 
Orthite,  287 
OLIVINE,  289 
GARNET,  290 
BIOTITE,  293 
Ilmenite,  303 
PYROXENES,  304 

AMPHIBOLES,  309 


IRON 

Hexagonal 

Cubic 

Orthorhombic 

Orthorhombic 

Cubic 

Tetragonal 
Cubic  . 
Hexagonal 
Amorphous? 
Hexagonal 
Monoclinic 
Monoclinic 
Monoclinic 
Cubic 
Cubic 
Cubic 
Cubic 

Orthorhombic 
Orthorhombic 
Monoclinic 
Monoclinic 
Orthorhombic 
Cubic 
Monoclinic 
Hexagonal 

Orthorhombic,  Mono- 
clinic,   and   Triclinic 
Orthorhombic,  Mono- 
clinic,  and  Triclinic 


FeS 

FeS2 

FeS2 

FeAsS 

CuxFe2Sx 

2+3 

CuFeS2 

M"4R'"2S7 

Fe2O3 

Fe2O3.H2O 

FeC03 

(Fe,Mn)WO4 

FeWO4 

FeSO4.7H2O 

(Fe,Mg)(A102)2,  etc. 

(Fe,Mn,Zn)(FeO2)2 

(Fe,Cr)[(Cr,Fe)02]2 

Fe(Fe02)2 

(Fe,Mn)[(Nb,Ta)O3]2 

HFeAl6Si2Oi3 

Ca2(Al,Fe)2(A1.0H)(Si04)3 

Ca2(Al,Ce,Fe)2(ALOH)(Si04)3 

(Mg,Fe)2Si04 

Fe3Al2(SiO4)3,  etc. 

(K,H)2(Mg,Fe)2(Al,Fe)2(Si04)3 

FeTi03 

(Mg,Fe)2(Si03)2,  etc. 

Ca(Mg,Fe)3(SiO3)4,  etc. 


350  MINERALOGY 

The  iron  ores  are  restricted  to  hematite,  limonite,  and  magnetite, 
with  hematite  by  far  the  most  important,  furnishing  annually  about 
94  per  cent,  of  all  the  iron  ore  mined.  Most  of  the  iron  ore  mined  is 
from  certain  well  defined  regions,  such  as  the  Lake  Superior,  the  Bir- 
mingham, and  the  Adirondack  districts.  The  Lake  Superior  district 
alone  produced  nearly  85  per  cent,  of  the  total  output  in  1917.  The 
average  prices  of  iron  ore  per  ton  for  the  whole  United  States,  were  $1.83 
in  1915,  $2.34  in  1916,  $3.15  in  1917,  and  $3.39  for  1918. 

The  mine  production  for  1917  (in  gross  tons)  of  the  various  districts 
is  shown  below. 

Production  in  Gross  Tons 

Lake  Superior  (Minnesota,  Michigan,  Wisconsin) 63,481,321 

Birmingham,  (Alabama) 6,187,073 

Chattanooga  (Tennessee,  Georgia,  North  Carolina) 821,485 

Adirondack  (New  York) 1,100,001 

Northern  New  Jersey  and  south  eastern  New  York 642,232 

Other  districts 3,056,739 


75,288,851 

The  total  production  in  1918  was  about  70,000,000  gross  tons,  or 
about  7  per  cent,  less  than  1917. 

LEAD 

GALENA,  212  Cubic  PbS 

Bournonite,  217  Orthorhombic  PbaC^SbaSe 

CERUSSITE,  251  Orthorhombic  PbCO3 

ANGLESITE,  267  Orthorhombic  PbSO4 

Crocoite,  258  Monoclinic  PbCrO4 

Wulfenite,  259  Tetragonal  PbMoO4 

PYROMORPHITE,  275  Hexagonal  Pb5Cl(PO4)3 

Vanadinite,  275  Hexagonal  Pb8Cl(VO4)3 

Galena  is  the  most  important  source  of  lead.  Large  quantities  of 
metallic  lead,  alloys  of  lead,  and  lead  pigments  are  consumed  annually  in 
the  trade.  Some  of  these  pigments  are  smelted  directly  from  the  ore, 
such  as  sublimed  white  lead  (lead  sulphate  75  per, cent.,  lead  oxide  20  per 
cent.,  and  zinc  oxide  5  per  cent.)  and  sublimed  blue  lead  (lead  sulphate 
50  to  53  per  cent.,  lead  oxide  38  to  41  per  cent.,  with  small  amounts  of  lead 
sulphide,  lead  sulphite,  and  zinc  oxide).  Pigments  chemically  prepared 
from  pig  lead  include  white  lead  (basic  carbonate),  red  lead,  and 
litharge. 

The  lead  ores  from  the  Mississippi  Valley  are  non-argentiferous  and 
the  lead  produced  from  them  is  designated  as  "soft"  lead,  in  distinction 
from  the  "hard"  lead  obtained  from  many  western  desilverized  lead  ores. 

In  1918  the  refined  lead  produced  from  domestic  ores  was  539,686 
short  tons,  obtained  principally  from  Missouri,  Idaho,  and  Utah.  In 
addition  100,008  short  tons  refined  lead  were  obtained  from  foreign  ores. 


CLASSIFICA  TION  OF  MINERALS  ACCORDING  TO  ELEMENTS     351 


LITHIUM 


TOURMALINE,  284 
Lepidolite,  297 
SPODUMENE,  308 


Hexagonal 
Monoclinic 
Monoclinic 


M/9Al3(B.OH)2Si4Oi9 
(Li,K)2(F,OH)2Al2Si309 
LiAl(SiO3)2 


The  chief  use  of  lithium  is  that  of  the  hydroxide  in  storage  batteries. 
The  bromide  and  iodide  are  used  in  photography,  the  cyanide  in  Roent- 
gen-ray experiments,  and  the  chloride  in  fire  works.  Synthetic  coal-tar 
products  are  gradually  replacing  the  lithium  salts  for  medicinal  purposes. 

The  production  of  lithium  minerals  in  United  States  is  not  large. 
In  1918  the  output  was  5,894  short  tons,  and  was  obtained  from  Cali- 
fornia and  South  Dakota. 


MAGNESIUM 


DOLOMITE,  245 
MAGNESITE,  246 
SPINELS,  267 
TOURMALINE,  284 
Chondrodite,  286 
OLIVINE,  289 
PYROPE,  292 
BIOTITE,  294 
PHLOGOPITE,  294 
CHLORITES,  297 
SERPENTINE,  297 

TALC,  299 
Sepiolite,  300 
Garnierite,  300 
PYROXENES,  304 

AMPHIBOLES,  309 


Hexagonal 

Hexagonal 

Cubic 

Hexagonal 

Monoclinic 

Orthorhombic 

Cubic 

Monoclinic 

Monoclinic 

Monoclinic 

Orthorhombic 

or  Monoclinic 
Monoclinic? 
Monoclinic? 
Unknown 
Orthorhombic 

and  Monoclinic 
Orthorhombic 

and  Monoclinic 


CaMg(C03)2 

MgC03 

Mg(A102)2,  «tc. 

M'9Al3(B.OH)2Si4019 

[Mg(F,OH)]2Mg3(Si04)2 

(Mg,Fe)2Si04 

Mg3Al2(Si04)3 

(K,H)2(Mg,Fe)2(Al,Fe)2(Si04)3 

(K,H)3Mg3Al(Si04)3 

H4Mg2Al2Si09 

H2Mg3Si4012 

H2Mg3Si4Oi2 
H4Mg2Si3010 
H2(Ni,Mg)SiO4 
Mg2(SiO3)2,  etc. 

(Mg,Fe)4(Si03)4,  etc. 


The  uses  and  production  of  magnesite  and  talc  only  will  be  discussed. 

Magnesite. — Nearly  all  magnesite  is  used  in  the  calcined  condition. 
Depending  upon  the  temperature  of  burning,  the  product  is  either 
"caustic"  calcined  or  "dead  burned"  magnesite.  The  "caustic" 
magnesia  results  from  a  moderate  heat  treatment  and  retains  from  3  to  8 
per  cent,  carbon  dioxide.  This  product  is  chemically  active,  combining 
readily  with  magnesium  chloride  forming  an  oxychloride,  or  Sorel  cement. 
This  cement  solidifies  into  an  extremely  hard  and  strong  mass  and  is  the 
basis  of  many  of  the  sanitary  flooring  preparations  placed  upon  the 
market  under  various  trade  names.  Fillers  in  this  cement  may  be  cork, 
talc,  asbestos,  clay,  marble  dust,  sand,  etc.  Magnesite  cement  floors  may 
be  laid  in  large  areas  without  cracking.  They  take  color  easily  and  are 
susceptible  to  polish.  It  is  claimed  the  surface  does  not  pulverize  or  dust. 

"Dead-burned"  magnesite  is  the  result  of  heating  to  incipient  fusion. 


352 


MINERALOGY 


The  product  is  chemically  inert.  This  material  is  employed  for  refractory 
purposes,  such  as  brick  and  linings  in  open  hearth  steel  and  electric  fur- 
naces, and  in  copper  converters.  As  a  refractory  substance  magnesia 
must  not  only  resist  corrosion  but  in  addition  must  possess  sufficient 
bonding  to  retain  its  form  in  the  furnace.  In  the  past  Austrian  and 
Hungarian  magnesites  have  been  preferred  for  this  purpose,  as  the  fusion 
of  6  to  8  per  cent,  of  iron  contained  in  them  increased  the  bonding  strength. 
Some  of  the  California  deposits  have  however  furnished  excellent  mate- 
rial for  refractory  purposes.  The  purer  magnesite  from  Greece  and 
California  has  been  employed  in  the  making  of  cement,  paints,  fire  proof 
coatings,  and  other  products. 

Magnesite,  raw  or  calcined,  is  also  used  in  the  manufacture  of  mag- 
nesium sulphate,  employed  in  medicine  and  the  textile  industries;  mag- 
nesium chloride,  for  making  Sorel  cement;  and  magnesium  bisulphate, 
for  disintegrating  wood  and  dissolving  the  non-cellulose  matter  in  the 
manufacture  of  wood  pulp  paper.  The  basic  carbonate  known  as  mag- 
nesia alba  is  used  in  fire-retarding  paint  and  as  a  non-conductor  of  heat 
in  coverings  for  steam  pipes. 

Metallic  magnesium  obtained  by  electrolytic  or  reduction  processes 
appears  to  have  a  brilliant  future,  especially  in  aeroplane  and  motor 
construction.  The  metal  is  reported  to  make  good  castings,  machines 
well,  is  about  J^  lighter  than  aluminum  and  from  two  to  four  times  as 
strong.  Alloys  of  magnesium  with  zinc  and  aluminum  can  readily  be 
prepared.  The  latter  is  known  as  magnaleum.  Metallic  magnesium  is 
also  used  for  scavenging  alloys  (removing  oxygen  and  nitrogen)  and 
during  the  war  was  in  very  great  demand  for  military  illumination  in 
the  form  of  shrapnel  trailers,  star  bombs,  and  flare  lights. 

The  domestic  production  of  magnesite  in  1918  was  obtained  from  Cali- 
fornia and  Washington,  while  Canada  furnished  most  of  the  imported 
material. 


Domestic  production 
(raw) 
(Short  tons) 

Imports 

Raw 
(Short  tons) 

Calcined 

(Short  tons) 

1916 

154,974 

75,345 

9,270 

1917 

316,838 

30,272 

3,965 

1918 

231,605 

5,432 

19,049 

Talc  and  Soapstone. — -Talc  and  soapstone  are  as  a  rule  not  found  to- 
gether. Vermont  and  New  York  are  the  leading  talc  producing  States, 
furnishing  in  1918  nearly  85  per  cent,  of  the  total  domestic  output,  which 
was  192,817  short  tons.  The  bulk  of  this  material  was  used  as  a  white 
filler  in  the  manufacture  of  paper.  For  this  purpose  talc  is  replacing 
china  clay  and  English  chalk.  Talc  is  also  used  for  foundry  facing, 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     353 

and  in  paints,  rubber  goods,  and  toilet  powders.  14,218  short  tons 
were  imported  in  1918,  chiefly  from  Canada,  Italy,  and  France.  Almost 
the  entire  supply  of  soapstone  in  United  States  was  obtained  from 
Nelson,  Albermarle,  and  Orange  counties,  Virginia.  The  total  yield 
of  soapstone  in  1918  was  13,955  short  tons,  which  was  largely  employed 
in  the  manufacture  of  laundry  tubs,  laboratory  table  tops,  sinks,  chemi- 
cal hoods,  fire  brick,  griddles,  and  so  forth. 

MANGANESE 

PYROLUSITE,  227  Orthorhombic?  MnO2 

MANGANITE,  234  Orthorhombic  MnO.OH 

RHODOCHROSITE,  248  Hexagonal  MnCO3 

Hausmannite,  253  Tetragonal  Mn2MnO4 

Psilomelane,  253  Unknown  MnO,BaO,H2O,etc. 

Huebnerite,  260  Monoclinic  MnWO4 

WOLFRAMITE,  261  Monoclinic  (Fe,Mn)WO4 

FRANKLINITE,  270  Cubic  (Fe,Mn,Zn)(FeO2)2 

COLUMBITE,  273  Orthorhombic  (Fe,Mn)[(Nb,Ta)O3]2 

SPESSARTITE,  292  Cubic  Mn3Al2(SiO4)3 

RHODONITE,  309  Triclinic  Mn2(Si03)2 

The  economic  demand  for  manganese  is  due  to  the  importance  of  its 
alloys,  especially  ferromanganese  and  spiegeleisen.  It  is  estimated  that 
in  recent  years  14  pounds  of  manganese,  in  the  form  of  an  alloy,  are  added 
to  every  ton  of  steel  produced.  Ferromanganese  contains  77  to  80  per  cent, 
manganese  and  is  used  in  making  open  hearth  steel,  while  spiegeleisen 
consists  of  from  12  to  33  per  cent,  manganese  and  finds  employment  in  the 
Bessemer  process.  The  role  of  manganese  is  to  produce  a  harder  steel 
and  at  the  same  time  act  as  a  deoxidizing  agent. 

The  oxide,  MnO2,  is  used  in  the  manufacture  of  chlorine  and  bromine, 
as  a  drier  in  paints  and  varnishes,  to  color  glass  and  pottery,  and  in  mak- 
ing flint  glass  and  dry  batteries.  For  dry  batteries  the  ore  should  con- 
tain at  least  80  per  cent.  MnO2,  less  than  1  per  cent,  iron,  and  under 
0.05  per  cent,  of  copper,  nickel,  or  cobalt. 

The  four  sources  of  manganese  in  United  States  are  (a)  Manganese 
ores  which  should  contain  40  per  cent,  manganese,  and  less  than  8  per  cent, 
silica  and  0.20  per  cent,  phosphorus;  (b)  Manganiferous  iron  ores,  which 
contain  12  to  25  per  cent,  manganese;  (c)  Manganiferous  silver  ores,  which 
are  largely  used  as  a  flux  but  at  intervals  smelted  to  spiegeleisen;  and 
(4)  Manganiferous  zinc  residues,  which  are  also  smelted  to  spiegeleisen. 

The  domestic  production  of  manganese  ores  is  by  no  means  equal  to 
the  demand,  and  importations  from  Brazil,  India,  and  Cuba  are  ab- 
solutely necessary.  Extensive  deposits  are  also  located  in  Russia.  The 
average  annual  production  in  United  States  for  thirty-five  years  (1880- 
1915)  was  10,645  tons,  but  under  the  stimulus  of  high  prices  it  is  esti- 
mated that  in  1918  the  output  was  about  330,000  long  tons. 

23 


354 


MINERALOGY 


PRODUCTION  AND  IMPORTATION  OF  MANGANESE  ORES  AND  ALLOYS  IN  UNITED  STATES, 

1917-1918,  IN  LONG  TONS 


Production 

Manganese  ore 

Ferromanganese 

Spiegeleisen 

Total 
imports 

Imports  from 

Production 

Imports 

Production 

Imports 

India       Brazil 

1917 
1918 

129,405 
305,869 

629,972 
491,303 

48,975 
29,275 

512,517 

345,877 

260,225 
306,076 

41,969 
26,906 

189,241 
263,861 

3,968 
1,969 

MERCURY 


CINNABAR,  215  Hexagonal 

TETRAHEDRITE,  218        Cubic 


HgS 

M"4R'"2S7 


Cinnabar  is  the  chief  source  of  mercury.  In  normal  times  between 
30-40  per  cent,  of  the  domestic  production  of  mercury  is  used  in  the  manu- 
facture of  mercuric  fulminate  for  explosive  caps,  one  flask  of  75  pounds 
making  100  to  120  pounds  of  detonator.  Mercury  is  also  employed  in 
the  extraction  of  gold  by  amalgamation  and  in  scientific  and  electrical 
apparatus.  The  chloride  (calomel)  is  used  for  medicinal  purposes,  and 
the  sulphide  (vermillion)  and  the  red  oxide  as  pigments. 

In  1918  the  production  of  mercury  in  United  States  was  32,883  flasks  of 
75  pounds  each,  valued  at  $3,863,752.  Of  this  amount  California  con- 
tributed 22,664  flasks,  Texas,  8,451  flasks,  and  Nevada,  Oregon,  Ari- 
zona and  Idaho,  smaller  amounts. 


MOLYBDENUM 


Molybdenite,  205 
Wulfenite,  259 


Hexagonal 
Tetragonal 


MoS2 
PbMoO4 


At  present  the  demand  for  molybdenum  is  not  great.  Its  chief  use 
is  in  the  manufacture  of  special  steels,  being  added  in  the  form  of  a 
f  erro-  or  manganese-molybdenum  alloy  (50  to  75  per  cent.  Mo) .  A  nickel- 
molybdenum  alloy  is  used  in  wire  drawing.  Sodium  and  ammonium 
molybdates  are  employed  to  some  extent  in  fire-proofing  fabrics,  and  in 
dyeing  leather,  silk,  and  wool.  As  a  lubricant,  molybdenite  is  preferable 
to  graphite,  especially  for  high  pressure  work. 

The  production  in  the  United  States  in  1918  was  equivalent  to  431 
short  tons  of  metallic  molybdenum.  The  ore  as  mined  is  of  low  grade, 
from  0.7  to  2.5  per  cent.  Mo,  but  deposits  are  known  in  Arizona,  Colorado, 
New  Mexico,  Utah,  California,  and  Montana. 


NICKEL 


Niccolite,  208  Hexagonal  NiAs 

Garnierite,  300  Unknown  H2(Ni,Mg)SiO4 

To  the  above,  nickeliferous  Pyrrhotite  should  be  added. 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     355 

The  demand  for  nickel  is  due  largely  to  the  importance  of  its  alloys. 
The  addition  of  from  2  to  3.50  per  cent,  of  nickel  to  steel  increases  both  its 
elasticity  and  tensile  strength.  Invar,  an  alloy  of  iron  containing  36 
per  cent,  nickel,  is  not  affected  by  temperature  changes  and  is  used  for 
scientific  instruments,  pendulums,  and  steel  tapes.  Other  important 
alloys  are  coinage  metal  (copper  and  nickel);  German  silver  (copper, 
zinc,  and  nickel) ;  Nichrome  (nickel  and  chromium)  used  as  a  substitute 
for  platinum  in  electrical  resistance,  crucible  triangles,  and  so  forth. 
Monel  is  obtained  by  smelting  the  Sudbury  ores  without  separating  the 
metals,  and  consists  of  67  per  cent.  Ni,  28  per  cent,  copper,  and  5  per  cent, 
other  metals,  mostly  iron  and  manganese.  This  alloy  has  a  tensile  strength 
equal  to  that  of  nickel  steel  and  is  very  resistive  to  corrosive  agents. 
It  is  used  for  propellers,  acid  pumps,  valves  on  high  pressure  steam  lines, 
valve  stems,  pickling  apparatus  for  sheet  and  tin  plate,  and  so  forth. 

The  world's  production  of  nickel  is  obtained  principally  from  the  copper 
and  nickel-ores  of  Sudbury  and  Cobalt,  Ontario,  and  from  the  garnierite 
ores  of  New  Caledonia.  Since  1909  no  nickel  ores  have  been  mined 
in  the  United  States,  although  in  1918  an  equivalent  of  441  short  tons  of 
nickel  was  obtained  as  a  by-product  in  the  electrolytic  refining  of  copper. 
Probably  one-third  to  one-half  of  this  amount  was  derived  from  imported 
ores.  The  imports  during  the  same  year  were  mainly  from  Canada, 
chiefly  in  the  form  of  ore  and  matte,  and  totaled  36,.603  short  tons. 

NIOBIUM 
COLUMBITE,  273  Orthorhombic  (Fe,Mn)[(Nb,Ta)O3]2 

Niobium  has  no  economic  importance  at  present.  Tantalum,  which 
is  nearly  always  present  in  niobium  minerals,  is  characterized  by  its 
extreme  hardness,  toughness,  and  high  melting  point.  It  is  used  in  the 
manufacture  of  drills,  files,  watch  springs,  pens,  rectifiers  for  alternating 
currents,  and  eleclric  lamp  filaments.  Tantalum  filaments  are  made  by 
pressing  a  mixture  of  the  oxide  and  paraffine  into  threads  which  are  then 
reduced  to  the  metal  by  the  passage  of  an  electric  current  in  a  vacuum. 

NITROGEN 
SODA  NITER,  241  Hexagonal  NaNO3 

While  small  quantities  of  sodium  nitrate  have  been  found  in  caves  and 
disseminated  through  clays  in  several  of  the  western  states,  no  deposits 
that  can  be  depended  upon  to  produce  considerable  amounts  have  been 
discovered  in  this  country.  Sodium  nitrate  is  obtained  almost  entirely 
from  the  arid  regions  of  northern  Chile.  The  crude  ore,  containing 
about  25  per  cent.  NaNOs,  yields  after  leaching  with  hot  water  a  product 
of  95  per  cent,  purity. 

In  normal  times  about  600,000  short  tons  of  niter  or  Chile  saltpeter 


356  MINERALOGY 

are  annually  imported.  This  is  used  principally  as  a  fertilizer  to  promote 
stalk  growth  in  plants,  and  also  in  the  manufacture  of  nitric  and  sulphuric 
acids.  In  1916,  due  to  the  unusual  demands  created  by  the  war,  the 
imports  increased  to  1,365,000  short  tons,  which  were  utilized  approxi- 
mately as  follows: 

Short  tons      Approximate  percentage 

Explosives 600',  000  45 

Fertilizers 280,000  20 

Manufacture  of  sulphuric  acid 85,000  5 

Miscellaneous,  including  stocks 400,000  30 


1,365,000  100 

PHOSPHORUS 

Monazite,  272  Monoclinic  (Ce,La,Di)PO4 

APATITE,  273  Hexagonal  Ga5F(PO4)3 

PYROMORPHITE,  275  Hexagonal  Pb5Cl(PO4)3 

Wavellite,  276  Orthorhombic  (A1.OH)3(PO4)2.5H2O 

Turquois,  276  Triclinic  H5[Al(OH)2]6Cu(OH)(PO4)4 

Plant  life  requires  soluble  phosphates  and  an  impure  variety  of  apatite, 
known  as  phosphate  rock,  furnishes  the  raw  material  to  supply  this  need. 
By  treating  the  raw  ground  rock  with  approximately  an  equal  weight  of 
sulphuric  acid,  a  superphosphate  is  formed  which  is  readily  assimilated 
by  plants.  Another  method  for  rendering  the  phosphorus  soluble  consists 
in  grinding  together  sodium  sulphate,  bituminous  coal,  and  phosphate 
rock.  When  this  dry  mixture  is  heated  in  a  rotary  kiln  under  proper 
temperature  and  oxidizing  conditions,  a  clinker  is  produced,  which  when 
finely  ground  contains  90  per  cent,  of  the  total  P2C>5  in  a  citrate-soluble 
form. 

Under  normal  conditions  the  United  States  produces  annually  about 
3,000,000  long  tons  of  phosphate  rock,  but  in  1918  due  to  the  decrease  in 
exports,  the  output  was  2,490,760  long  tons.  Of  this  amount  Florida 
furnished  82  per  cent,  and  Tennessee  15  per  cent.  Enormous  deposits  of 
phosphate  rock  have  been  located  in  the  western  states,  particularly  in 
Idaho,  Utah,  Wyoming,  and  Montana,  but  the  production  thus  far  from 
these  western  localities  is  insignificant.  At  the  present  rate  of  consump- 
tion it  is  estimated  that  the  western  states  alone  could  supply  the  world's 
demand  for  about  900  years. 

PLATINUM 
NATIVE  PLATINUM,  196  Cubic  Pt 

Some  of  the  important  uses  of  platinum  are  in  the  contact  process 
for  manufacturing  concentrated  sulphuric  acid,  and  in  the  fixation  of 
nitrogen.  Because  of  its  high  fusibility  and  resistance  to  acids,  platinum 
is  in  great  demand  in  the  manufacture  of  chemical,  physical,  and  elec- 
trical apparatus.  It  is  also  employed  in  certain  parts  of  the  ignition 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     357 


systems  of  internal  combustion  engines.  The  jewelry  trade  has  likewise 
in  the  past  consumed  large  amounts,  estimated  at  50  per  cent,  of  the 
total  platinum  used  in  this  country.  As  iridium  imparts  hardness  to 
platinum,  the  so-called  platinum  used  in  electrical  work  and  by  jewelers  is 
an  alloy  of  platinum  and  iridium,  containing  from  10  per  cent,  to  50  per 
cent,  of  the  latter  element.  The  high  price  of  platinum  in  recent  years 
has  greatly  stimulated  research  for  suitable  substitutes,  and  alloys  of 
palladium  with  gold  and  silver,  tungsten,  and  molybdenum  have  in 
certain  instances  replaced  the  more  expensive  metal. 

The  disintegration  of  basic  magnesium  rocks,  such  as  peridotite, 
dunite,  and  pyroxenite,  containing  disseminated  platinum,  has  lead  to 
the  concentration  of  the  metal  in  platinum  placers.  In  normal  times 
about  95  per  cent,  of  the  world's  supply  is  obtained  from  the  Ural  Moun- 
tains in  Russia,  but  it  is  estimated  that  at  the  rate  of  production  before 
the  war  and  with  present  methods  of  recovery,  these  deposits  will  be 
exhausted  in  about  twelve  years. 

The  United  States  produces  a  very  small  amount  of  the  platinum 
consumed.  In  1917,  only  605  troy  ounces  of  crude  platinum  were  re- 
covered, mainly  from  the  placers  in  Alaska,  California,  Oregon,  and 
Washington,  although  a  gold-platinum-palladium  mine  in  Clark  County, 
Nevada,  and  a  copper  mine  in  Wyoming  were  also  contributors.  In 
addition  38,831  troy  ounces  of  refined  metals  of  the  platinum  group  were 
obtained  as  by-products  in  the  refining  of  copper  matte  and  gold  bullion. 
A  considerable  amount  of  secondary  platinum  is  also  recovered  from  the 
refining  of  scrap  and  sweeps. 

The  world's  production  of  crude  platinum,  in  troy  ounces,  since  1914  is 
given  below : 


Country 

1914 

1915 

1916 

1917 

Canada 

30 

100 

60 

80 

Columbia  

17,500 

18,000 

25,000 

32,000 

New  South  Wales  j 
Tasmania                /  ' 

1,248 

303 

222 

no  estimate 

Russia 

241  200 

124  000 

63  900 

50  000 

United  States  

570 

742 

750 

605 

260,548 

143,145 

89,932 

82,685 

ALUNITE,  262 
MICAS,  293 
NEPHELITE,  301 
LEUCITE,  313 
ORTHOCLASE,  316 
MICROCLINE,  318 
APOPHYLLITE,  326 


POTASSIUM 

Hexagonal 

Monoclinic 

Hexagonal 

Orthorhombic 

Monoclinic 

Triclinic 

Tetragonal 


K2(A1.2OH)6(SO4)4 

(K,H)2(Mg,Fe)2(Al,Fe)2(SiO4)3etc. 

(Xa,K)8Al8Si9034 

K2Al2Si4Oi2 

KAlSi3O8 


H14K2Ca8(SiO3)16.9H2O 


358  MINERALOGY 

Potassium  chloride  and  sulphate  are  used  in  large  quantities  as  ferti- 
lizers. Other  potassium  salts  are  also  quite  essential  in  certain  industries. 
Thus,  caustic  potash  is  used  in  the  manufacture  of  the  better  grades  of 
soap;  the  hydrated  carbonate  in  cut  glass,  optical  glass,  and  incandescent 
light  bulbs;  the  chlorate  in  matches;  the  nitrate  in  black  powders;  the 
bichromate  in  dyeing  and  tanning;  the  cyanide  as, a  solvent  in  extracting 
gold  from  ores;  the  ferricyanide  in  photography.  While  medicinal  and 
other  chemical  uses  also  demand  varying  amounts  of  potassium  salts. 

Prior  to  the  war  United  States  imported  over  270,000  short  tons  of 
K2O.  Practically  the  entire  supply  used  in  this  country  was  then  ob- 
tained from  the  famous  Stassfurt  deposits  of  Germany.  With  this  source 
not  available  the  domestic  production,  which  in  1918  was  equivalent 
to  54,562  short  tons  of  K20  valued  at  $21,437,300,  was  derived  from: 

Natural  salts  or  brines 39,716 

Alunite 2,621 

Dust  from  cement  mills  and  blast  furnaces 1,779 

Kelp 4,804 

Wood  ashes 1,213 

Distillery  waste  (molasses) 3,467 

Other  sources. .  962 


54,562 

The  imports  in  1918  amounted  to  only  7,957  short  tons  of  K20,  valued 
at  $8,907,836. 

SILICON 

QUARTZ,  220  Hexagonal  SiO2 

OPAL,  232  Amorphous  SiO2.xH2O 

Silicon  is  also  an  essential  constituent  of  all  silicates. 

The  greatest  demand  for  quartz  comes  from  the  building  trade. 
The  value  of  sandstone  (including  quartzite)  sold  in  United  States  in 
1917  was  $5,512,421,  which  represented  6.7  per  cent,  of  the  total  value  of 
all  stone  sold  that  year.  The  three  leading  states  which  contributed 
nearly  70  per  cent,  of  the  total  value  of  sanstone  were  Pennsylvania, 
Ohio,  and  New  York. 

Some  varieties  of  quartz,-  as  well  as  opal,  are  prized  as  gems  and 
the  value  of  their  output  in  1918  was  estimated  at  $21,515. 

SILVER 

NATIVE  SILVER,  199  Cubic  Ag 

Argentite,  213  Cubic  Ag2S 

Proustite,  217  Hexagonal  Ag3AsS3 

Pyrargyrite,  217  Hexagonal  Ag3SbS3 

TETRAHEDRITE,  218  Cubic  M'^R^jS, 

Cerargyrite,  238  Cubic  AgCl 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     359 

The  four  most  important  sources  of  silver  in  United  States,  which  in 
1917  furnished  over  98  per  cent,  of  the  total  output,  were  dry  or  siliceous 
ores  (30.4  per  cent.),  copper  ores  (28.8  per  cent.),  lead  ores  (27  per  cent.), 
and  lead-zinc  ores  (12.2  per  cent.) 

Siliceous  ores  are  those  consisting  mainly  of  quartz  with  small  amounts 
of  gold  and  silver.  Some  of  the  chief  deposits  of  this  type  are  at  Tonopah, 
Nevada;  San  Juan,  Leadville,  and  Aspen,  Colorado;  and  in  Granite, 
Jefferson,  and  Silver  Bow  counties,  Montana.  The  important  silver 
bearing  copper  ores  are  found  at  Butte,  Montana;  in  the  Bingham  and 
Tintic  districts,  Utah;  and  at  Bisbee  and  Jerome,  Arizona.  Deposits 
of  argentiferous  galena  are  mined  in  the  Coeur  d'Alene  district,  Idaho; 
Bingham  and  Tintic  districts,  Utah;and  at  Aspen  and  Leadville,  Colorado. 

The  total  domestic  production  in  1§17  was  71,740,362  ounces  valued 
at  $59,078,100,  of  which  the  following  six  States  were  the  most  important 
producers. 

Montana 14,555,034  ounces 

Utah 13,360,905  ounces 

Idaho 11,402,542  ounces 

Nevada 11,217,654  ounces 

Colorado 7,291,495  ounces 

Arizona. 6,962,257  ounces 

The  production  in  1918  amounted  67,879,206  ounces. 


SODIUM 


HALITE,  236 
CRYOLITE,  240 
SODA  NITER,  241 
NEPHELITE,  301 
Cancrinite,  302 
Sodalite,  303 
Lazurite,  303 

Pectolite,  307 
ALBITE  and 

PLAGIOCLASES,  319 
SCAPOLITE,  322 
Natrolite,  324 
ANALCITE,  325 
STILBITE,  326 


Cubic 

Monoclinic 

Hexagonal 

Hexagonal 

Hexagonal 

Cubic 

Cubic 

Monoclinic 
Triclinic 

Tetragonal 
Orthorhombic 
Cubic 
Monoclinic 


NaCl 

AlF3.3NaF 

NaNOs 

(Na,K)8Al8Si9034 

H6(Na2,Ca)4(NaC03)2Al8Si903« 

Na4Al2(AlCl)(SiO4)3 

(Na2,Ca)2Al2[Al(NaS04,NaS3,Cl)] 

(Si04)3 

(Ca,Na2)2(Si03)2 
NaAlSisOg,  etc. 

Ca4Al6Si6O25,  etc. 
Na2Al(AlO)(SiO3)3.2H2O 
Na2Al2(Si03)4.2H20 
(Ca,Na2)Al2Si8Oi6.6H2O 


Halite  or  salt,  as  produced  in  this  country,  is  of  two  types,  either  rock 
salt  or  brine  salt.  Rock  salt  occurs  in  beds  and  is  mined  by  means  of 
shafts  in  a  manner  similar  to  that  of  coal.  The  output  of  rock  salt  in 
1918  was  1,683,941  short  tons.  Brine  salt  may  be  made  from  natural  or 
artificial  brines.  In  the  majority  of  cases  fresh  water  is  forced  through 
drill  holes  to  the  salt  beds  and  the  artificial  brine  then  pumped  to  the 
surface.  The  salt  is  obtained  by  the  evaporation  of  the  brine  by  either 


360  MINERALOGY 

solar  or  vacuum  pan  processes.  Other  chemical  products  produced 
from  the  brine  include  salt  cake,  soda  ash,  caustic  soda,  sodium  bicar- 
bonate, sodium  acetate,  sodium  chlorate,  sodium  phosphate,  Glauber's 
salt,  calcium  chloride,  chlorine,  and  hydrochloric  acid. 

United  States  furnishes  practically  all  the  salt  consumed  in  this 
country  and  the  supply  seems  inexhaustible.  In  the  single  State  of  New 
York  an  area  of  approximately  2000  square  miles  is  underlain  with  salt, 
the  thickness  of  which  varies  from  8  to  318  feet. 

The  domestic  production  in  1918  was  7,238,744  short  tons,  (equiva- 
lent to  over  50,000,000  bbl.  of  280  Ibs.),  which  was  an  increase  of  3.7 
per  cent,  in  quantity  and  35.1  per  cent,  in  value  over  the  production  in 
1917.  Although  fifteen  States  reported  a  production,  the  four  leading 
producers  were: 

Michigan : 2,403,125  short  tons 

New  York !  . 2,130,530  short  tons 

Ohio 1,089,887  short  tons 

Kansas 819,504  short  tons 

STRONTIUM 

STRONTIANITE,  250  Orthorhombic  SrCO3 

CELESTITE,  255  Orthorhombic  SrSO4 

Before  the  war  the  entire  supply  of  celestite  and  strontianite  was 
imported  from  Germany,  England,  and  Sicily.  With  the  curtailment  of 
shipments  from  those  sources  domestic  deposits  of  a  commercial  nature 
were  located  in  southern  California,  Washington,  and  Texas.  The 
carbonate  is  the  more  valuable  ore  as  it  can  be  easily  converted  into  the 
various  salts,  but  the  sulphate  is  much  more  abundant.  In  1917  about 
4,035  short  tons  of  strontium  ore  were  mined  in  the  United  States,  of 
which  about  10  per  cent,  was  strontianite  and  the  balance  celestite. 
Strontium  salts  are  used  in  pyrotechnics,  for  the  recovery  of  sugar  in 
beet-sugar  refineries,  and  in  medicine.  In  1918  the  production  fell  to 
400  short  tons. 

SULPHUR 

NATIVE  SULPHUR.  193     Orthorhombic  S 

Lazurite,  303  Cubic  (Na8,Ca)»AL»[Al(NaS04,NaS,,Cl] 

(Si04)3 
Sulphur  is  also  an  essential  constituent  of  sulphides  and  sulphates. 

Deposits  of  native  sulphur  in  Louisiana  and  Texas  furnish  more  than 
99  per  cent,  of  the  entire  output  of  this  country.  Occurrences  of  minor 
importance  are  known  in  Wyoming,  Utah,  Nevada,  California,  Colorado, 
and  Oregon.  The  production  of  sulphur  in  1918  was  1,353,525  long  tons. 
Under  normal  conditions  the  bulk  of  the  sulphur  employed  in  the  manu- 
facture of  sulphuric  acid  is  obtained  from  pyrite,  and  copper  and  zinc 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS     361 

bearing  sulphides  which  are  burned  to  sulphur  dioxide.  In  1918  the 
domestic  production  of  pyrite  was  455,432  long  tons,  while  496,792 
tons  were  imported,  mainly  from  Spain  and  Portugal.  In  the  manu- 
facture of  paper  it  is  estimated  that  one-eighth  of  a  ton  of  sulphur  is 
used  for  each  ton  of  sulphite  pulp  produced. 

It  is  estimated  that  in  1917  the  production  of  sulphuric  acid  consisted 
of  5,967,551  tons  of  a  strength  of  50°  Baume  (62.18  per  cent.  H2SO4) 
and  of  759,039  tons  of  a  strength  higher  than  66°  Baume  (93.19  per  cent. 
H2S04).  The  50°  acid  is  used  largely  in  the  manufacture  of  fertilizers, 
sulphate  of  ammonia,  and  alum;  while  the  more  concentrated  acid  is 
employed  in  the  steel  industry  (for  pickling  purposes),  for  the  purification 
of  petroleum,  and  in  the  manufacture  of  explosives. 

TIN 
CASSITERITE,  226  Tetragonal  SnO2  or  SnSnO4 

While  cassiterite  is  rather  widely  disseminated,  in  a  few  places  only 
are  the  occurrences  of  commercial  importance.  The  production  in  the 
United  States  is  insignificant  when  compared  with  the  consumption  of 
the  metal,  which  under  normal  condition  is  approximately  50,000  tons 
annually.  Deposits  have  been  worked  intermittently  in  South  Dakota, 
Texas,  North,  and  South  Carolina.  Alaska  is  at  present  a  more  consist- 
ent producer  and  in  1918  its  output  was  equivalent  to  68  tons  of  metallic 
tin. 

The  World's  chief  sources  of  tin  ore  are  the  Malay  States,  Bolivia, 
Australia,  and  Cornwall,  England.  In  1917  the  production  was  distri- 
buted as  follows: 

Short  tons  of 
metallic  tin 

Malaya  Spates 49,000 

Bolivia 29,300 

Banka : 14,000 

Siam 9,400 

China 9,000 

Australia •. 6,000 

Nigeria .. . .- 6,000 

Billiton '...-?..,.  5,500 

Cornwall 4,600 

South  Africa y-.'. ..  2,000 

Other  countries 2,000 

In  1918  the  world's  production  was  slightly  less  than  that  indicated 
above. 

TITANIUM 

RUTILE,  224  Tetragonal  TiO2  or  TiTiO4 

Ilmemte,  303  Hexagonal  FeTiO3 

TITANITE,  323  Monoclinic  CaSiTiO5 

The   demand   for   titanum  is  not  very  great.     Rutile  and  ilmenite 


362  MINERALOGY 

are  both  used  in  making  ferrotitanium  which  when  added  to  Bessemer 
steel  serves  as  a  deoxidizing  agent  and  increases  its  tensile  strength. 
Rutile  is  also  the  source  of  titanium  for  cuprotitanium  used  in  brass  and 
other  copper  bearing  alloys.  Titanium-aluminum  bronze,  which  is 
extremely  resistant  to  the  action  of  sea  water  and  chemical  liquors,  pos- 
sesses physical  properties  equalling  those  of  phosphor  and  manganese 
bronze,  although  it  is  considerably  lighter  than  either. 

In  1918  the  Virginia  mines  reported  a  production  of  261  short  tons 
of  rutile  valued  at  $39,150.  The  rutile  carries  about  95  per  cent,  of  Ti02. 
In  the  concentration  process  a  considerable  quantity  of  ilmenite  is  also 
recovered  as  a  by-product. 

TUNGSTEN 

Scheelite,  259  Tetragonal  CaWO4 

Huebnerite,  260  Monoclinic  MnWO4 

WOLFRAMITE,  261  Monoclinic  (Fe,Mn)WO4 

Ferberite,  261  Monoclinic  FeWO4 

While  in  foreign  countries  wolframite  is  the  most  important  ore  of 
tungsten,  in  the  United  States  both  scheelite  and  ferberite  surpass 
it  in  importance.  Over  90  per  cent,  of  the  tungsten  mined  is  converted 
into  ferro-alloys  and  tungsten  steels.  American  high-speed  tool  steels, 
which  are  capable  of  holding  their  temper  at  a  red  heat,  contain  about 
18  per  cent,  tungsten,  4.5  per  cent,  chromium,  and  0.6  per  cent,  vanadium. 
In  some  cases  3  to  5  per  cent,  of  cobalt  is  also  added.  These  steels  are  also 
used  for  armor  plate  and  projectiles.  Tungsten  alloys  readily  with  many 
metals  and  some  of  these  have  been  proposed  as  substitutes  for  platinum, 
particularly  a  tungsten-molybdenum  alloy  for  dental  work. 

The  production  of  tungsten  ores  in  the  United  States  in  1918  was 
equivalent  to  5,041  short  tons  of  concentrates  containing  60  per  cent. 
WO8  valued  at  $6,802,000.  The  imports  during  1918  were  11,750  tons 
of  ore  valued  at  $11,409,237.  The  domestic  production  is  obtained 
mainly  from  Boulder  Country,  Colorado,  and  from  the  Atolia  district, 
California.  Important  foreign  deposits  are  located  in  Burma,  Portugal, 
Australia,  Bolivia,  and  Argentina. 

URANIUM 

Uraninite,  262  Cubic  UO3,UO2,PbO,  etc. 

Carnotite,  277  Orthorhombic  K2O.2UO3.V2O6.3H2O? 

Ferro-uranium  is  used  in  high  speed  steel  and  aluminum-uranium  in 
non-ferrous  alloys.  In  special  steels  a  small  percentage  of  uranium  may 
be  substituted  for  tungsten,  while  in  non-ferrous  alloys  it  is  beneficial 
because  of  its  deoxidizing  properties.  Uranium  compounds  are  employed 
to  some  extent  in  coloring  glass  yellow  with  a  green  reflex;  in  photography; 


CLASSIFICA  TION  OF  MINERALS  ACCORDING  TO  ELEMENTS     363 

in  the  ceramic  industry  to  impart  yellow,  brown,  gray,  and  velvety  tints; 
and  as  a  mordant  for  silk  and  wool.  Radium  is  sometimes  recovered 
from  uranium  minerals.  The  amount  present  is  extremely  small,  about 
one-third  of  a  milligram  of  radium  in  one  kilogram  (2.2046  Ibs.)  of  uranium. 
When  uranium  is  used  as  an  illuminant  the  radium  salt  is  usually  mixed 
with  artificial  zinc  sulphide  and  some  cementing  material,  such  as  amyl 
acetate.  The  alpha  rays  given  off  by  the  radium  salt  strike  the  particles 
of  zinc  sulphide  and  cause  them  to  glow. 

Carnotite  from  southwestern  Colorado  and  southeastern  Utah  is 
the  chief  domestic  source  of  uranium  compounds  and  in  1918  the  output 
was  equivalent  to  105.5  tons  of  UaOg  containing  27.1  grams  of  radium. 


VANADIUM 

Vanadinite,  275  Hexagonal  Pb5Cl(VO4)3 

Carnotite,  277  Orthorhombic  K2O.2UO3.V2O5.3H2O? 

Roscoelite,  296  Monoclinic  H8K2(Mg,Fe)(Al,V)4(SiO3)2? 

The  most  important  use  of  vanadium  is  in  the  manufacture  of  special 
steels,  where  it  not  only  removes  the  objectionable  elements  oxygen  and 
nitrogen,  but  the  small  amount  (about  0.22  per  cent.)  remaining  in 
the  steel  increases  its  tensile  strength  and  resistance  to  shock.  Vanadium 
steel  is  extensively  used  for  locomotive  and  automobile  cylinders,  pistons 
and  bushings,  and  also  for  high  speed  tools,  die  blocks,  and  so  forth. 
Because  of  their  strength  and  toughness  vanadium  bronzes  are  suitable 
for  trolley  wheels  and  bronze  gears.  Vanadium  compounds  are  employed 
in  ceramics  to  produce  a  golden  glaze,  in  the  preparation  of  indelible  ink, 
for  fixing  aniline  black  on  silk,  and  as  a  catalytic  agent  in  the  manufacture 
of  sulphuric  acid. 

About  80  per  cent,  of  the  world's  supply  of  vanadium  is  derived 
from  the  sulphide  (VS4?),  patronite,  which  occurs  in  quantity  only  at 
Minasragra,  Peru.  The  chief  domestic  source  of  the  metal  and  its  com- 
po'unds  is  the  vanadium  mica,  roscoelite.  Subordinate  amounts  are 
obtained  from  carnotite  and  vanadinite.  Roscoelite  is  mined  principally 
in  the  vicinity  of  Placerville  and  Vanadium,  San  Miguel  County,  Colorado, 
where  it  occurs  in  small  bands  in,  and  disseminated  throughout,  a  greenish 
sandstone.  The  rock  averages  from  1  to  1J£  per  cent,  vanadium.  In 
1918  the  equivalent  of  276  tons  of  vanadium  was  produced  in  the  United 
States. 

ZINC 

SPHALERITE,  205  Cubic  ZnS 

TETRAHEDRITE,  218  Cubic  M"4R'"2S7 

Zincite,  228  Hexagonal  ZnO 

SMITHSONITE,  247  Hexagonal  ZnCO3 

FRANKLINITE,  270  Cubic  (Fe,MnZn)(FeO2)2 

HEMIMORPHITE,  280  Orthorhombic  H2Zn2SiO5 

Willemite,  289  Hexagonal  Zn2SiO4 


364  MINERALOGY 

In  normal  times  about  60  per  cent,  of  the  spelter  (zinc)  output  is 
used  for  galvanizing,  20  per  cent,  in  making  brass,  11  per  cent,  is  rolled 
into  sheet  zinc,  1  per  cent,  for  desilverizing  lead,  and  8  per  cent,  for  all 
other  purposes.  Zinc  dust  is  used  for  precipitating  gold  from  cyanide 
solutions,  and  some  of  the  zinc  compounds  are  employed  as  pigments. 
The  four  white  pigments  involving  the  use  of  zinc  are,  zinc  oxide  (zinc 
white),  leaded  zinc  oxide,  zinc-lead  oxide,  and  lithopone.  Lithopone  is  a 
mixture  obtained  by  chemical  precipitation  of  zinc  sulphide  and  barium 
sulphate. 

The  chief  zinc  producing  regions  in  the  United  States  are  : 

Joplin  district  (Missouri,  Kansas,  Oklahoma)  producing  about  25  % 

Franklin  Furnace  District  (New  Jersey)  producing  about  20  % 

Butte  District  (Montana)  producing  about  20  % 

Mississippi  Valley  District  (Wis.,  Iowa,  111.)  producing  about  5  to  10% 

Leadville  district  (Colorado)  producing  about  5  to  10  % 

Coeur  d'Alene  district  (Idaho)  producing  about  5  to  10% 

In  1913  the  domestic  production  of  zinc  was  337,252  short  tons,  which 
in  1918  was  increased  to  492,405  short  tons.  The  production  in  1915, 
in  terms  of  the  metal,  of  the  more  important  producing  states,  together 
with  the  quantity  of  recoverable  zinc  contained  in  the  crude  ore  is 
given  below. 

Missouri 136,300  short  tons;  1.3%  Wisconsin 41,403  short  tons ;  2.1  % 

New  Jersey..  116,618  short  tons;15.8%  Idaho 35,077  short  tons;  10. 1  % 

Montana ....   93,573  short  tons;13 . 2  %  Tennessee 16,461  short  tons;  3.1% 

Colorado 52,297  short  tons;19 . 5  %  Kansas 14,365  short  tons;  2.0% 

The  recoverable  zinc  content  of  the  ores  varied  from  32.8  per  cent, 
in  Nevada  to  1.3  per  cent,  in  Missouri,  giving  an  average  for  the  entire 
United  States  of  2.7  per  cent. 

ZIRCONIUM 
ZIRCON,  225  Tetragonal  ZrSiO4 

The  uses  of  zirconium  and  its  compounds  are  very  limited.  The 
addition  of  small  amounts  of  zirconium  to  steels,  brass,  and  copper  is 
claimed  to  secure  sound  castings  and  to  increase  their  strength  and  re- 
sistance to  acids.  Cooperite  is  an  alloy  of  zirconium  and  nickel,  and  is 
very  resistant  to  acids  and  alkalis.  It  is  also  recommended  for  use  in  the 
manufacture  of  machine  and  cast  tools.  As  its  heat  conductivity  is 
higher  than  for  other  high  speed  metals  the  cutting  efficiency  is  increased. 
Increasing  the  amount  of  zirconium  in  the  alloy  increases  the  hardness 
but  decreases  the  melting  point  and  tensile  strength.  Cooperite  is 
claimed  to  be  self -hardening  and  no  tempering  is  necessary.  The  oxide, 
zirconia,  glows  intensely  when  heated  and  therefore  has  been  used  for 
coating  the  lime  and  magnesia  pencils  used  in  the  Drummond  or  "lime" 
light.  The  filaments  of  the  Nernst  lamp  consist  mainly  of  .zirconia  with 


CLASSIFICATION  OF  MINERALS  ACCORDING  TO  ELEMENTS      365 

variable  amounts  of  yttria,  erbia,  thoria,  and  ceria.  The  oxide  is  also 
used  as  an  opacifier  in  enamel  ware,  as  a  permanent  white  pigment  not 
affected  by  acids  or  alkalies,  as  a  polishing  powder,  and  for  refractory 
purposes. 

The  chief  source  is  the  oxide,  baddeleyite,  found  in  quantity  in  Minas 
Geraes,  Brazil.     The  mineral  zircon  was  formerly  an  important  source. 


GLOSSARY 

This  glossary  contains  all  the  important  terms  used  in,the  descriptive  and  determin- 
ative portions  of  the  book.     See  the  index  for  page  references  to  other  terms. 

Acicular — needle-like. 

Acute — sharply  pointed. 

Adamantine  luster — like  that  of  the  diamond,  or  oiled  glass. 

Aggregate — mass,  cluster,  group. 

Alkaline  taste — like  that  of  soda. 

Allochromatic — having  a  color  which  is  not  an  inherent  property  of  the  mineral, 
but  due  to  pigments,  inclusions,  or  other  impurities,  hence,  variable. 

Alluvial — relating  to  deposits  made  by  flowing  water. 

Amorphous — devoid  of  crystallinity. 

Amygdaloid — igneous  rock  containing  small  cavities,  which  are  filled  entirely,  or 
in  part,  with  minerals  of  secondary  origin. 

Arborescent — branching,  tree-like. 

Argillaceous — clay-like  odor. 

Asterism — a  star-like  effect  seen  in  either  transmitted  or  reflected  light. 

Astringent  taste — causing  contraction  or  puckering. 

Basal — parallel  to  the  basal  pinacoid. 

Basalt — basic  igneous  rock,  dark  and  compact. 

Bipyramid — two  pyramids  placed  base  to  base. 

Bisphenoid — four-sided  form  of  the  tetragonal  system,  each  face  being  an  isosceles 
triangle. 

Bituminous — odor  due  to  the  presence  of  bitumen  or  other  organic  matter. 

Bladed — elongated  and  flattened,  like  a  knife  blade. 

Botryoidal — closely  united  spherical  masses,  resembling  a  bunch  of  grapes. 

Brachypinacoid — form  with  two  faces  in  the  orthorhombic  or  triclinic  systems, 
parallel  to  the  brachy  and  vertical  axes. 

Brittle — crumbles  under  knife  or  hammer,  cannot  be  cut  into  slices. 

Capillary — hair-  or  thread-like. 

Carbonatization — formation  of  carbonates. 

Cellular — porous,  like  a  sponge. 

Chatoyant — having  a  changeable,  undulating,  or  wavy  coior  or  luster. 

Clastic — made  up  of  fragments. 

Clay — fine,  soft,  aluminous  sediments  that  are  plastic. 

Cleavable — capable  of  splitting  in  definite  directions. 

Cleavage — property  of  many  crystalline  substances  of  breaking  or  splitting  in 
definite  directions,  yielding  more  or  less  smooth  surfaces. 

Clinopinacoid — form  with  two  faces  in  the  monoclinic  system,  parallel  to  the 
clino  and  vertical  axes. 

Columnar — long  thick  fibers,  often  paralielly  grouped. 

Compact — closely  or  firmly  united. 

Complex  crystals — highly  modified,  having  many  crystal  forms  or  faces. 

Concentric — spherical  layers  about  a  common  center,  similar  to  layers  of  an  onion. 

Conchoidal — curved,  shell-like. 

Concretion — rounded  mass  formed  by  accumulation  about  a  center. 

Concretionary — formed  as  a  concretion. 

366 


GLOSSARY  367 

Confused — indistinct,  jumbled  together. 

Conglomerate — sedimentary  rock,  composed  of  rounded  fragments,  coarse  or  fine. 

Contact  mineral — formed  under  the  influence  of  an  igneous  intrusion. 

Crested — tabular  crystals  arranged  in  ridges. 

Cruciform — in  the  form  of  a  cross,  cross-shaped. 

Cryptocrystalline — finely  crystalline,  revealed  only  under  the  microscope. 

Crystal — substance  bounded,  entirely  or  partially,  by  natural  plane  surfaces. 

Crystalline — having  crystal  structure,  but  without  definite  geometrical  form. 

Crystallization — process  of  solidification  in  the  form  of  well  developed  crystals, 
or  in  crystalline  masses. 

Crystallography — study  of  crystal  forms  and  properties. 

Cubical — with  the  form  of  a  cube. 

Cyclic — repeated  twinning  yielding  circular  forms. 

Dendritic — branching,  fern-like. 

Diaphaneity — ability  to  transmit  light. 

Dichroism — property  of  exhibiting  different  colors  by  transmitted  light  when 
viewed  in  two  perpendicular  directions. 

Disseminated — scattered  through  a  substance. 

Divergent — radiating  from  a  center. 

Dodecahedral — pertaining  to  the  rhombic  dodecahedron,  a  form  with  twelve  faces 
in  the  cubic  system. 

Domatic — relating  to  a  dome,  a  hoiizontal  prism. 

Drusy — rough  surface  due  to  a  large  number  of  small,  closely  crowded  crystals. 

Ductile — capable  of  being  drawn  into  wire.     Ductile  substances  aie  also  malleable 
and  sectiie. 

Dull  luster — not  bright  or  shiny. 

Earthy — without  luster,  dull. 

Efflorescence — thin  crust  or  coating,  often  powdery. 

Elastic — resumes  original  position  when  displaced. 

Eruptive  rock — formed  by  the  solidification  of  a  surface  flow  of  molten  rock. 
Often  used  as  a  synonym  of  igneous. 

Etched — corroded. 

Felted— filers  closely  matted. 

Ferruginous — containing  iron. 

Fetid — emitting  an  offensive  odor. 

Fibrous — consisting  of  slender  fibers  or  filaments. 

Fissure — crack  or  crevice. 

Flexible — capable  of  bending  without  breaking,  and  does  not  resume  original 
position  when  the  force  is  removed. 

Fluorescence — property  of  emitting  light  when  exposed  to  electrical  discharges, 
or  when  heated. 

Folia — having  the  form  of  thin  plates  or  leaves. 

Foliated — in  plates  or  leaves  which  separate  easily. 

Fossiliferous — containing  or  composed  of  fossils. 

Fracture — refers  to  surface  obtained  when  breaking  in  a  direction  other   than 
parallel  to  cleavage  or  parting. 

Friable — easily  crumbled  or  reduced  to  powder. 

Furrowed — deeply  striated,  grooved. 

Gangue — associates  of  more  valuable  minerals  or  ores. 

Garlic — odor  observed  when  arsenic  minerals  are  heated. 

Globular — spherical  or  nearly  so. 

Gneiss — laminated  or  foliated  metamorphic  rock  consisting  usually  of  quartz, 
feldspar,  and  mica. 


368  MINERALOGY 

Granite — coarsely  crystalline  igneous  rock,  consisting  usually  of  quartz,  feldspar 
(orthoclase),  and  mica  or  hornblende. 

Granular — consisting  of  closely  packed  grains,  either  coarse  or  fine. 

Guano — excrement  of  sea  fowl. 

Habit — development  or  form  of  crystals. 

Hackly — rough  surface,  covered  with  sharp  points. 

Hardness — resistance  offered  to  abrasion  or  scratching. 

Hemimorphic — having  different  planes  about  the, two  ends  of  a  crystallographic 
axis. 

Hexoctahedron — form  of  the  cubic  system  having  forty-eight  faces. 

Hopper  shaped — cavernous  and  tapering,  square  funnel  shaped. 

Hydration — combining  chemically  with  water. 

Hygroscopic — property  of  absorbing  moisture  from  the  atmosphere. 

Idiochromatic — minerals  with  a  constant  color,  an  inherent  property. 

Igneous  rock — one  formed  by  the  solidification  of  a  molten  mass  from  within  the 
earth. 

Impregnated — finely  disseminated  and  intimately  mixed  with  rock. 

Impressed — marked  by  pressure,  indented. 

Inclusion — foreign  material  enclosed  within  a  mineral. 

Incrustation — crust  or  coating  on  another  substance. 

Inelastic — not  elastic. 

Interlaced 


,  intertwined,  confused. 
Interwoven  J 

Iridescence — showing  play  of  colors,  usually  due  to  thin  film  or  coating. 
Isochromatic — lines  or  sections  possessing  the  same  color. 

Kimberlite — altered,  very  basic  igneous  rock,  consisting  essentially  of  serpentine, 
olivine,  augite,  pyrope;  sometimes  diamond-bearing. 

y   small,  thin  plates  or  layers,  curved  or  straight. 

Lamellar — consisting  of  lamella?  or  laminae. 

Lava— molten  rock,  especially  surface  flows;  also  applied  to  the  solidified  product. 

Lenticular — le  ns-shaped . 

Limestone — rock  composed  essentially  of  calcium  carbonate,  calcite. 

Luster — manner  in  which  the  surface  reflects  light. 

Macropinacoid — form  with  two  faces  in  the  orthorhombic  or  triclinic  systems, 
parallel  to  the  macro  and  vertical  axes. 

Macroscopic — visible  to  the  unaided  eye,  opposed  to  microscopic. 

Malleable — capable  of  being  flattened  by  hammering. 

Mammillary — rounded  mass,  larger  than  that  of  a  grape. 

Marble — recrystallized  limestone  or  dolomite;  may  also  include  other  limestones 
susceptible  to  a  polish,  and  serpentine. 

Massive — without  definite  crystal  form;  either  crystalline  or  amorphous. 

Meager — rough  touch. 

Metallic  luster — simulating  a  metal  and  exhibited  by  minerals  which  are  opaque 
or  nearly  so,  and  quite  heavy. 

Metalloidal — having  the  appearance  of  a  metal. 

Metamorphic  rock — one  that  has  been  altered  by  heat,  pressure,  liquids,  or  gases, 
so  as  to  render  its  texture  either  crystalline  or  schistose. 

Meteorite — mass  of  stone  or  iron  which  has  fallen  to  the  earth  from  outer  space. 

Micaceous — composed  of  very  thin  plates  or  scales,  like  those  of  mica. 

Mimicry — imitation  of  forms  of  a  higher  symmetry  by  those  of  lower  grade  of 
symmetry,  usually  the  result  of  twinning. 

Modified,  highly — consisting  of  a  large  number  of  crystal  forms  or  faces. 


GLOSSARY  369 

Monochromatic — homogeneous  light  of  a  definite  wave-length. 

Mottled— spotted. 

Multi-colored — having  many  colors. 

Neolithic — later  stone  age,  that  of  smooth  or  polished  stone  implements. 

Nodular    1 

.         >  rounded  mass  of  irregular  shape. 

Nugget — rounded,  irregular  lump,  especially  of  a  metal. 

Ocherous — earthy,  and  usually  red,  yellow,  or  brown  in  color. 

Octahedral — pertaining  to  the  octahedron,  eight-sided  form  of  the  cubic  system. 

Oolitic — rounded  particles  the  size  of  fish-eggs. 

Opalescent — with  milky  or  pearly  reflections. 

Opaque — -will  not  transmit  light  even  through  thin  layers  or  edges. 

Orthopinacoid — form  with  two  faces  in  the  monoclinic  system,  parallel  to  the 
ortho  and  vertical  axes. 

Oxidation — combing  chemically  with  oxygen. 

Paleolithic — earlier  stone  age,  that  of  rough  stone  implements. 

Parameters — linear  intercepts  of  a  crystal  face  on  the  crystallographic  axes. 

Parting — false  cleavage,  usually  the  result  of  twinning. 

Pearly — similar  to  the  luster  of  the  mother  of  pearl. 

Peat — dark  brown  to  black  substance,  formed  by  the  partial  decomposition  of 
vegetable  tissue  in  marshes. 

Pegmatite — very  coarse  grained  acid  igneous  rock,  consisting  essentially  of  quartz, 
feldspar,  and  mica. 

Peridotite — very  basic  igneous  rock,  composed  largely  of  olivine  and  augite  or 
hornblende. 

Phanerocrystalline — crystals  or  coarsely  crystalline. 

Phonolite — compact  extrusive  rock,  consisting  essentially  of  orthoclase,  nephelite, 
and  pyroxene. 

Pinacoidal — relating  to  forms  with  two  planes,  parallel  to  two  or  more  crystallo- 
graphic axes. 

Pisolitic — composed  of  small,  rounded  masses,  the  size  of  peas. 

Pitchy — resembling  pitch. 

Placers — sands  and  gravels  containing  minerals  of  economic  importance. 

Plastic — capable  of  being  molded  or  shaped. 

Plates- — broad,  relatively  thin  masses. 

Platy — consisting  of  plates. 

Plumose — feathery. 

Pocket — cavity  in  a  rock,  often  filled  with  minerals. 

Polysynthetic — consisting  of  thin  lamellae  due  to  repeated  twinning. 

Prismatic — elongated  parallel  to  one  of  the  crystallographic  axes,  usually  the 
vertical  axis. 

Pseudo — false. 

P       d  h         f  P°ssessing  the  geometrical  form  of  another  mineral. 

Pungent — sharp,  biting. 

Pyramidal — pertaining  to  the  pyramid,  a  form  which  usually  intersects  three 
crystallographic  axes. 

Pyritohedron — form  of  the  cubic  system  with  twelve,  five-sided  faces. 

Rectangular — intersecting  at  90°. 

Reduction — loss  of  oxygen  chemically. 

Refraction,  double — yielding  two  refracted  rays. 

Reniform — large,  rounded  masses,  kidney-shaped. 

Resinous — luster  of  resin,  greasy. 


370  MINERALOGY 

Reticulated — fibers  crossing  like  a  net. 

Rhombic — diamo  nd-shaped . 

Rhombohedral — relating  to  the  rhombohedron,  a  form  of  the  hexagonal  system, 
with  six  faces  intersecting  at  angles  other  than  90°. 

Rosette — simulating  a  rose. 

Saline — salty. 

Sandstone — sedimentary  rock  consisting  of  consolidated  sand. 

Scalenohedral — relating  to  the  scalenohedron,  a  twelve-sided  form  of  the  hexa- 
gonal system,  each  face  being  a  scalene  triangle. . 

Scaly — consisting  of  scales. 

Schiller — peculiar  bronze-like  luster. 

Schist — metamorphic  rock  with  foliated  or  parallel  structure,  splitting  easily  along 
certain  planes. 

Seam — narrow  vein. 

Sectile — capable  of  having  slices  cut  off. 

Semi-opaque — between  opaque  and  transparent. 

Shale — laminated  sedimentary  rock,  consisting  of  hardened  muds,  silts,  or  clays. 

Sheaf -like — resembling  a  sheaf  of  wheat. 

Silky — luster  of  silk,  due  to  fibrous  structure. 

Skeletal — pertaining  to  crystals  with  incomplete  development  of  their  faces,  often 
with  cavernous  appearance. 

Slate — dense,  fine  grained  metamorphic  rock,  which  splits  easily  into  broad,  thin 
layers  or  sheets. 

Splendent — very  bright  by  reflected  light. 

Splintery — breaking  into  splinters. 

Stalactitic — cylindrical  or  conical  masses  resembling  icicles. 

Stalky — consisting  of  long,  stout  fibers. 

Stellate — radiating  from  a  center  producing  star-like  forms. 

Streak — color  of  fine  powder,  usually  obtained  by  rubbing  the  mineral  on  unglazed 
porcelain. 

Subadamantme — imperfectly  adamantine. 

Subconchoidal — imperfectly  conchoidal. 

Sublimation — direct  solidification  from  a  vapor. 

Submetallic — imperfectly  metallic. 

Syenite — granular  igneous  rock,  commonly  consisting  of  orthoclase,  and  hornblende 
or  biotite. 

Tabular— flat,  tablet-like. 

Tarnish — thin  film  formed  on  the  surface  when  exposed  to  air  and  different  in 
color  from  that  of  the  fresh  fracture. 

Terminations — faces  on  the  end  of  a  crystal. 

Tetragonal  trisoctahedron — form  of  the  cubic  system  with  twenty-four  trapezo- 
hedral  faces. 

Tetrahedral — pertaining  to  the  tetrahedron,  a  four-sided  form  of  the  cubic  system. 

Tetrahexahedron — form  of  the  cubic  system  with  twenty-four  triangular  faces. 

Tough — not  easily  broken. 

Translucent — when  light  passes  through,  but  objects  can  not  be  seen  distinctly. 

Transparency — refers  to  the  amount  of  light  passing  through  a  substance. 

Transparent — when  sufficient  light  passes  through  the  substance  so  that  objects 
tnay  be  distinctly  seen. 

Trap — dark,  basic,  fine  grained  igneous  rock. 

Trichroism — property  of  exhibiting  different  colors  by  transmitted  light  when 
viewed  in  three  perpendicular  directions. 

Trillines — intergrowth  of  three  crystals  in  a  symmetrical  manner. 


GLOSS. 4MY  371 

Twinned — crystals  consisting  of  more  than  one  individual,  arranged  in  a  definite 
manner. 

Twins — Symmetrical  intergrowth  of  two  crystals. 

Variegated — with  different  colors. 

Vein — crack  or  fissure,  partially  or  completely  filled  with  mineral  matter. 

Vitreous  luster — like  that  of  glass. 

Warty — small,  rounded  masses  resembling  warts. 

Waxy — luster  of  wax. 

Zonal — in  zones  or  layers. 


TABULAR  CLASSIFICATION  SHOWING  ELEMENTS 

OF  'SYMMETRY  AND  THE  SIMPLE  FORMS  OF 

THE  THIRTY-TWO  CLASSES  OF  CRYSTALS 

(Pages  372  to  378). 


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Scalenohedral 
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Bipyramidal 
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Trapezohedral 

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Pyramidal 
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with  Hemimorphi 

Tetragonal 
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(  Tetartohedrism] 

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378 


Tables  for  the  Determination  of  the  150  Minerals 

Described  in  This  Text  by  Means  of  Their 

Physical  Properties,  Occurrences, 

and  Associates 

(Pages  380  to  647). 


379 


380  GENERAL  CLASSIFICATION 

A.  MINERALS  WITH  METALLIC  LUSTER 


Color  of  mineral 


Streak 


Hardness     Page 


1.  Dark  gray  or  black. 


White,  gray,  green,  red,  brown, 
or  yellow 


Black.. 


1  to  3  382 
3  to  6  384 
Over  6  390 


1  to  3 
Over  3 


394 
398 


2.  Metallic  white  or  light  me- 
tallic gray 


Metallic  white  or  steel  gray. 


Black. 


1  to  6 


f      Ito 
' '  \      Ove 


3 
Over  3 


402 

402 
404 


{Brown  or  yellow 1  to  6  406 

Black Over3  406 

t  Gray,  red,  or  yellow ' 1  to  3  408 

4.  Brass,   bronze,    or   copper  \ 

red  I  Black Over  3  408 

White,  gray,  green,  red,  brown,  j  3  fc°  g  4U 

5.  Red,  brown,  or  blue or  yellow  1  Over  6  418 

Black..  Ito  6  420 


AND  ANALYTICAL  KEY.  381 

B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Color  of  mineral 


Streak 


Hardness     Page 


1.  Dark  gray  or  black. 


Green,  red,  brown,  yellow,   or  f      1  to  6          422 


black 


f      1  to 
I      Ove 


Over  6         426 


1  to  3          428 

Uncolored,  wHte,  or  light  gray.  -|      3  to  6          430 

Over  6        432 


2.  Pink,  red,  or  red  violet. . . 


Red,  brown,  or  yellow. 


1  to  3          438 
Over  3         440 


Uncolored,  white,  or  light  gray. 


r      Ito 

|      3to 

Ove 


1  to  3          444 
6          446 
Over  6         452 


3.  Green,  blue,  or  blue  violet . 


Blue,  green,  brown,  or  yellow. . .         1  to  6  460 

Ito  3  464 

Uncolored,  white,  or  light  gray.  \      3  to  6  468 

Over  6  478 


4.  Yellow  or  brown. 


Red,  brown,  or  yellow 


1  to  3  486 

Over  3         488 


Ito  3          492 

Uncolored,  white,  or  light  gray.  \      3  to  6          498 

Over  6        608 


5.  Colorless,   white,   or  light  / 

<  Lncolored,  white,  or  light  gray.  \      3  to  6          524 

Ov«r  6         538 


382 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak  —  White,  gray,  green,  red,  brown,  or  yellow 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CHLORITE  (Procblorite, 

clinocblorite) 
H8Mg5Al2Si3018? 


Monoclinic  Dull  Black 

C — Tabular,  six-sided,  Sub  metallic      Greenisb 

often  bent  and  Translucent       black 
twisted  to  opaque 

M— Foliated,  scaly, 
granular,  earthy 


297 


HEMATITE,  variety               Hexagonal  Metallic            Iron  black 

Specular  iron  ore      C — Tbin  tabular,  often  Splendent         Dark  steel 

Fe2O3                                              in  parallel  position  Opaque,  to         gray 

M — Scaly,  micaceous,  translucent 
platy,  foliated 


230 


BIOTITE  (Black  mica) 

(K,H)2(Mg,Fe)2(Al,Fe)2 
(Si04)3 


Monoclinic  Submetallic  Black 

C — Tabular,   witb   hex-  Pearly  Brownish 

agonal  or  rhombohe-  Opaque  to  black 

dral  habit  transparent  Greenish 

M — Plates,  disseminated  black 
scales 


294 


Pyrargyrite 

Ag3SbS3 

217 


Hexagonal  Metallic  Dark  lead 

C — Small,  complex,  Adamantine       gray 

bemimorphic,  rare  Opaque  to 
M — Compact,  dissemi-        transparent 
nated,  bands,  crusts 


SILVER 
Ag 


Cubic  Metallic  -  Dark  gray  to 

C — Small,  often  dis-  Opaque  black  after 

torted  exposure, 

M — Grains,  scales,  plates,  otherwise 

twisted  hair- or  wire-  silver    white 

like  forms 


199 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


383 


1.          Pale  green 
2.5 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Basal,  perfect; 
when  foliated, 
conspicuous 
F — Scaly,  earthy 
Tough  to  brittle 


2 . 6  Laminae  are  flexible  but  in- 
3 .  elastic,  with  sligh  tly  soapy 
feel.  Common  in  schists 
and  serpentine.  With 
magnetite,  garnet,  diop- 
side,  magnesite.  Often 
as  a  scaly  or  dusty  coating 
on  other  minerals.  Pseu- 
domorphous  after  garnet. 


Cherry  red 
Reddish  brown 


C — None,  but  dis- 
tinct parting 
F — Uneven 
Brittle  to  elastic 


4.9  Bright, -shiny  scales,  often 
5.3  loosely  compact;  foliated 
or  micaceous  masses.  In 
metamorpbic  rocks  or  as 
sublimation  product 
around  volcanoes. 


2.5        White 
3.          Grayish 


C — Basal,  perfect,          2 . 7      Easily  recognized  by  struc- 


conspicuous 

Tough,   laminae  of 

fresh  biotite 

very  elastic 


3 . 2  ture,  highly  perfect  cleav- 
age, and  elasticity.  Im- 
portant constituent  of 
many  igneous  and  meta- 
morphic  rocks — granite, 
syenite,  gneiss. 


2.5        Cherry  red 

C  —  Imperfect 

5  .  8      Frequently  as  gray  or  dark 

3.          Purplish  red 

F  —  Conchoidal 

red  bands,  known  as  dark 

Brittle 

ruby  silver  ore.   With  prou- 

stite;  in  veins  with  other 

silver  minerals  and  galena. 

2.5 
3. 


Silver  white 
Light  lead  gray 


C— None  10. 

F— Hackly  12. 

Malleable,  ductile 


Color  and  streak  darken  on 
exposure.  With  silver, 
lead,  arsenic,  cobalt,  and 
nickel  minerals — argen- 
tite,  pyrargyrite,  prous- 
tite,  galena,  smaltite;  also 
fluorite,  calcite,  barite. 


384 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

TETRAHEDRITE                    Cubic                                     Metallic            Dark    steel 
C  —  Tetrahedral,  often        Opaque                gray 
Cu8Sb2S7                                       highly  modified                                    Iron  black 
M  —  Granular,  compact 

218 


Uraninite  (Pitchblende) 
UO3,  UO2,  PbO,  etc. 

262 

Cubic                                     Pitch-like 
C  —  Octahedral,  rare            Submetallic 
M  —  Botryoidal,     colum-  Dull 
nar,  curved  lamellar  ;  Opaque 
granular,     compact; 
apparently       amor- 
phous. 

Pitch  black 
Brownish 
black 
Greenish 
black 

SIDERITE 

FeCO3 

248 

Hexagonal                             Metalloidal 
C  —  Rhombohedral,  curv-  Dull 
ed  or  saddle-shaped,  Opaque  to 
common                          translucent 
M  —  Cleavable,  granular, 
compact,  botryoidal, 
rarely  fibrous 

Brownish 
black 
Black 

SPHALERITE  (Black  Jack) 
ZnS 

205 

Cubic                                      Submetallic 
C  —  Tetrahedral,  com-       Resinous 
mon,  often  very           Opaque  to 
complex                          translucent 
M  —  Compact,  cleavable, 
fine  or  coarse  granu- 
lar 

Black 
Yellowish 
black 
Brownish 
black 

MANGANITE 
MnO.OH 

234 

Orthorhombic                      Metallic 
C  —  Columnar,  prismatic,  Submetallic 
vertically     striated;  Opaque 
often   in  groups   or 
bundles 
M  —  Columnar,  granular, 
stalactitic 

Iron  black 
Dark  steel 
gray 

TITANITE  (Sphene) 
CaTiSiO6 

323 

Monoclinic                           Submetallic 
C  —  Wedge-  or  envelope-  Vitreous 
shaped     when     dis-  Opaque  to 
seminated,     tabular     translucent 
or    prismatic    when 
attached 
M  —  Compact,  lamellar 

Black 
Brownish 
black 

1.  DARK  GRAY  OR  BLACK  IN  COLOR 


385 


Hardness  3  to  6 


Hard-             Str 

ness 

Cleavage  =  C 
eak                  Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.          Reddish  brown      C  —  Indistinct 

4.3 

Crystals    have     character- 

4. 

F  —  Uneven 

5.4 

istic     tetrahedral     habit. 

Brittle 

Sometimes    coated    with 

chalcopyrite.  With  sphal- 

erite, galena,  bournonite, 

chalcopyrite,  siderite. 

3.          Dark  brown           F  —  Conchoidal,  un- 

4.8 

Pitch-like  appearance  and 

6.5       Olive  green                   even 

9.7 

fracture  important.  Fresh 

Brittle 

material     is     hard     and 

heavy.    With  ores  of  lead, 

silver,  and  bismuth;  also 

orthite. 

3.5       Yellowish  brown  C — Rhombohedral, 
4.  perfect,       con- 

spicuous 

F — Conchoidal 

Brittle 


3.7  Distinguished  from  sphal- 
3.9  erite  by  curved  crystals 
and  rhombohedral  cleav- 
age. In  ore  deposits; 
beds  and  concretions  hi 
limestones  and  shales. 
With  pyrite,  chalcopyrite, 
galena,  tetrahedrite,  cryo- 
lite. 


3.5 

4. 


Dark  brown 
Yellowish  brown 
Grayish 


C — Dodecahedral, 
perfect,  usually 
conspicuous 

F — Conchoidal 

Brittle 


3 . 9  Color  and  streak  vary  with 
4 . 2  impurities.  Extensively 
in  limestone.  With 
galena,  chalcopyrite,  py- 
rite, barite,  fluorite,  sider- 
ite, rhodochrosite. 


3.5       Reddish  brown 
4.          Blackish  brown 

C  —  Brachypina- 
coidal,  perfect 
F  —  Uneven 
Brittle 

4.2 
4.4 

Alters  ea-sily  to  pyrolusite, 
hence,  surface  may    give 
black  streak.     With  other 
manganiferous    minerals; 
also  barite,  calcite,  sider- 
ite. 

5. 
5.5 


White 
Gray 


C — Prismatic  3.4      Generally  in  crystals.  With 

F — Conchoidal  3.6       feldspars,  pyroxenes,  am- 

Brittle  phiboles,  chlorite,  scapo- 

lite,  zircon,  apatite. 


386 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

LIMONITE 
Fe2O3.H2O 


235 


C — Always    p  s  e  u  d  o-  Metallic 
morphs,     commonly  Dull 
after  pyrite,  marca-  Opaque 
site,  siderite 

M — Compact,  stalactitic, 
botryoidal,  renif orm ; 
often  with  internal, 
radial  fibrous  struc- 
ture 


Black 
Brownish 
black 


Hausmannite 
Mn2MnC>4 

253 


Tetragonal  Metallic  Black 

C — A  cute  pyramidal,  Greasy  Brownish 

cyclic  twins  not  un-  Opaque  black 

common 
M — Granular,  compact 


Huebnerite 
MnW04 

260 


Monoclinic  Submetallic      Brownish 

C — Long  fibrous,  bladed,  Resinous  black 

stalky;  often  diver-  Translucent      Black 

gent,   without  good     to  opaque 

terminations 
M — Compact,    lamellar, 

granular 


WOLFRAMITE 

(Fe,Mn)WO4 

261 


Monoclinic  Submetallic      Dark  gray 

C — Thick  tabular,  short  Metallic  Brownish 

columnar,  often  Opaque  black 

large  Iron  black 

M — Bladed,  curved  lam- 
ellar, granular 


Ferb  erite 
FeWO4 

261 


Monoclinic  Submetallic 

C — Wedge  shaped,  short  Splendent 

prismatic,  tabular        Opaque 
M — Fan  shaped    aggre- 
gates, bladed.  granu- 
lar, compact 


Iron  black 
Brownish 
black 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


387 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

5.          Yellowish  brown   F  —  Conchoidal,               3  .  6      Often  with  black  varnish- 
5.5                                              splintery                    4.          like  surface,  passing  ink 
Brittle                                           the  soft,  yellow  earthy  01 

ocherous  variety.  With 
pyrite,  hematite,  magne- 
tite, siderite.  Pseudo- 
morphs  after  pyrite  very 
common. 


5. 
6.5 


Chestnut  brown 


C — Basal,  perfect 
F — Uneven 
Brittle 


4 . 7  Steep,     horizontally     stri- 

4.8  ated,    octahedral-like   bi- 
pyramids    and    complex 
twins.     With  manganese 
mineral  s — pyrolusite, 
psilomelane,   braunite; 
magnetite,  barite,  hema- 
tite. 


5.          Yellowish  brown    C — Clinopinacoidal, 
6.5       Greenish  gray  perfect,  con- 

spicuous. 
Brittle 


6.7  Structure,  cleavage,  and 
7.3  specific  gravity  impor- 
tant. Compare  wolfram- 
ite. In  quartz  veins,  with 
fluorite,  pyrite,  scheelite, 
galena,  tetrahedrite. 


6. 
5.5 

Dark  red  brown     C  —  Clinopinacoidal, 
perfect,  con- 
spicuous. 
F  —  Uneven 
Brittle 

7  .  1      Distinguished  from  hueb- 
7  .  5        nerite  by  streak.  Powder 
may  be  slightly  magnetic. 
With  cassiterite,   quartz, 
mica,     fluorite,     apatite, 
scheelite,      molybdenite, 
huebnerite,  chalcopyrite. 

5. 
5.5 

Dark  brown           C  —  Clinopinacoidal, 
perfect. 
F  —  Uneven 
Brittle 

7.5      In    granites    and    pegma- 
tites.    With  quartz,  chal- 
copyrite,   galena,    scheel- 
ite. 

388 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

HORNBLENDE  (Amphi-        Monoclinic  Submetallic  Pitch  black 

bole)   C — Long  prisfnatic,  prism  Vitreous  Greenish 
Silicate  of  Ca,  Mg,  Fe,  A*!,           angle     124°;     often  Opaque  to          black 

etc.  with  rhombohedral-     translucent  Brownish 

like  terminations  black 

M — Bladed,  fibrous, 
312  granular,  compact 

AUGITE  (Pyroxene)  Monoclinic  Submetallic  Pitch  black 

C — Short  prismatic,  Vitreous  Greenish 

Silicate  of  Ca,  Mg,  Fe,  Al,  thick  columnar,  Opaque  to          black 

etc.  prism  angle  87°  translucent  Brownish 

M — Compact,    granular,  black 

disseminated 


Psilomelane 

Amorphous  ?                        Metallic 

Iron  black 

M  —  Botryoidal,    r  e  n  i-  Dull 

Bluish  black 

MnO2,  BaO,  H2O,  etc. 

form,         stalactitic;  Opaque 

Dark  gray 

253 

smooth  surfaces 

Ilmenite  (Menaccanite) 

Hexagonal                            Metallic 

Iron  black 

C  —  Thick  tabular,               Submetallic 

Brownish 

FeTiOs 

rhombohedral              Opaque 

black 

M  —  Thin  plates,  granu- 

lar,    compact  ;     dis- 

seminated grains; 

303 

pebbles  or  sand 

CHROMITE 

Cubic                                    Submetallic 

Iron  black 

C  —  Octahedral,  rare            Pitchy 

Brownish 

(Fe,Cr)  [(Cr,Fe)02]2 

M  —  Compact,    granular,   Opaque 

black 

disseminated 

270 


Orthite  (Allanite) 

Ca2(Al,Ce,Fe)2(Al.OH) 
(Si04)3 


Monoclinic  Submetallic  Black 

C — Tabular,  rare  Greasy  Pitch  black 

M — Compact,    granular,  Opaque  to  Brownish 

bladed,  disseminated     translucent  black 

grains 


287 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


380 


Hardness  3  to  6 


Hard- 
Streak 
ness 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

5.          Gray 

C  —  Prismatic,   per- 

2.9 

Simple,     pseudohexagonal 

6.          Grayish  green 

fect,    conspicu- 

3.3 

crystals  and  cleavages  at 

Grayish  brown 

ous—  124° 

56°  and    124°  important. 

Yellow 

Brittle 

Very     common     and     in 

nearly  all  types  of  rocks. 

With    calcite,    feldspars, 

quartz,  pyroxenes,  chlorite. 

5.          Grayish  green 

C  —  Prismatic,   per- 

3.2 

Crystals      usually      eight- 

6.          Gray 

fect,    conspicu- 

3.6 

sided,   more  rarely  four- 

ous  —  87° 

sided.     Pseudotetragonal, 

Brittle 

with  prism  angles  of  87° 

and    93°.    Cleavage   less 

distinct    than    on    horn- 

blende.   Common  in  basic 

eruptive  rocks  and  crys- 

talline limestones. 

5.          Dark  brown 

F  —  Conchoidal,  un- 

3.7 

Often  with  fine  sooty  coat- 

6.         Blackish  brown 

even 

4.7 

ing  of  pyrolusite.     With 

Brittle 

other     manganese     min- 

erals; limonite,  barite. 

5.          Dark  brown 

C  —  None,   partings 

4.3 

Often    slightly    magnetic. 

6.          Reddish  brown 

may  be  noted 

5.5 

With    hematite,    magne- 

F —  Conchoidal 

tite,    apatite,   serpentine, 

Brittle 

titanite,    rutile.        Com- 

mon in  black  sands. 

6.6        Dark  brown 
Grayish  brown 

C  —  Octahedral,  in- 
distinct 
F  —  Uneven,      con- 
choidal 
Brittle 

4.3      May  be  slightly  magnetic. 
4  .  6        Pitch-like        appearance. 
With     serpentine,      talc, 
chrome    garnet;   also    in 
black  sands    and     plati- 
num placers. 

6.6      Grayish 
6.          Brownish  gray 
Pale  brown 

C  —  Pinacoidal,    in- 
distinct 
F  —  Uneven,       con- 
choidal 
Brittle 

3.        Often  coated  with  yellow- 
4.           ish    or    brownish    altera- 
tion    product.     Dissemi- 
nated in  the  more   acid 
igneous    rocks;     also    in 
limestones.     With     mag- 
netite,    epidote,     quartz, 
feldspars. 

300 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

HEMATITE,  varieties  Hexagonal  Metallic  Iron  black 

Specular  iron  ore  C — Pyramidal,     tabular,  Dull  Reddish 

Fe2O3  Compact  rhombohedral  Opaque  black 

Martite  M — Compact,    granular,  Dark  steel 

Argillaceous  micaceous,      colum-  gray 

nar,    radiated    reni- 
form  or  botryoidal 


230 


FRANKLINITE 

(Fe,Mn,Zn)(FeO2)2 


270 


Cubic  Metallic 

C — Octahedrons,  alone  or  Dull 

with   dodecahedron;  Opaque 

often  with  rounded 

edges 
M — Compact,    granular, 

rounded  grains 


Iron  black 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


HEMATITE,  varieties  Hexagonal  Metallic 

Specular  iron  ore  C — Pyramidal,     tabular,   Dull 


Fe2O3       Compact 
Martite 
Argillaceous 


rhombohedral  Opaque 

M — Compact,  granular, 
micaceous,  colum- 
nar, radiated  reni- 
form  or  botryoidal 


Iron  black 
Reddish 

black 
Dark  steel 

gray 


230 


FRANKLINITE 

(Fe,Mn,Zn)(FeO2)2 

270 


Cubic  Metallic 

C — Octahedrons,  alone  or  Dull 

with   dodecahedron;  Opaque 

often  with  rounded 

edges 
M — Compact,    granular, 

rounded  grains 


Iron  black 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


391 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

5.5        Cherry  red              C  —  None,     parting        4.9      Specular  iron  ore,  crystals 
6.          Reddish  brown             sometimes                 5.3        or    sparkling    scales    and 

noted 

F — Uneven 
Brittle 


grains,  often  with  irides- 
cent tarnish;  compact  hem- 
atite, fibrous,  columnar, 
reniform;  martite,  octahe- 
dral crystals,  pseudomor- 
phous  after  magnetite;  ar- 
gillaceous hematite,  impure 
from  sand,  clay,  jasper. 


5.5 
6. 


Reddish  brown 
Dark  brown 


C — Octahedral,  in- 
distinct 

F — Conchoidal 
Brittle 


5 .  Powder  frequently  slightly 
5 . 2  magnetic.  Distinguished 
by  associates — willemite 
(yellow  to  green),  zincite 
(red),  rhodonite  (flesh 
red),  calcite. 


Hardness  over  6 


6. 
6.5 


Cherry  red 
Reddish  brown 


C — None,     parting 

sometimes 

noted 
F — Uneven 
Brittle 


4.9  Specular  iron  ore,  crystals 
5.3  or  sparkling  scales  and 
grains,  often  with  irides- 
cent tarnish;  compact 
hematite,  fibrous,  colum- 
nar, reniform;  martite,  oc- 
tahedral crystals,  pseudo- 
morphous  after  magne- 
tite; argillaceous  hematite, 
impure  from  sand,  clay, 
jasper. 


6. 
6.5 


Reddish  brown 
Dark  brown 


C — Octahedral,  in- 
distinct 
F — Conchoidal 
Brittle 


5 .  Powder  frequently  slightly 
5 . 2  magnetic.  Distinguished 
by  associates — willemite 
(yellow  to  green),  zincite 
(red),  rhodonite  (flesh 
red),  calcite. 


392 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak  —  White,  gray,  green,  red,  brown,  or  yellow 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

COLUMBITE  (Tantalite) 
(Fe,Mn)[(Nb,Ta)03]2 


273 


Orthorhombic  Submetallic       Iron  black 

C — Short  prismatic,  tab-  Greasy  Brownish 

ular  Dull  black 

M — Compact,      dissemi-  Opaque 

nated 


RUTILE 

TiO2  or  TiTiO4 

224 


Tetragonal  Metallic  Iron  black 

C — Prismatic,    vertically  Adamantine      Brownish 

striated;       twinned,  Opaque  to          black 

yielding  knee-shaped  translucent     Reddish 
or  rosette  forms  black 

M — Compact,      dissemi- 
nated 


CASSITERITE,  varieties         Tetragonal  Submetallic      Black 

Ordinary     C — Thick  prismatic,   Dull  Brownish 

SnO2  or  Stream  tin  knee-shaped     twins,   Translucent        black 

SnSnO4  common  to  opaque 

M — Compact,  reniform, 
botryoidal,  rounded 
pebbles 

226 

GARNET,  varieties  Cubic  Submetallic      Velvet  black 

Andradite    C — Dodecahedrons,     te-  Translucent      Brownish 
R3"R2'"(SiO4)3  Almandite  tragonal   trisoctahe-     to  opaque         black 

R"  =  Ca,Fe,Mg  drons,    alone    or    in 

R'"  =  Al,Fe  combination,     com- 

mon 

M — Granular,    compact, 
lamellar,       dissemi- 
290  nated,  sand 


TOURMALINE 

M9/Al3(B.OH)2Si4O19 
M'  =  Na,K,Li,Mg,Fe 


284 


Hexagonal  Submetallic 

C — Prismatic,    vertically  Pitchy 
striated,  terminated  Opaque 
with       broken       or 
rhombohedral-like 
surfaces 

M — Compact,  divergent 
columnar,  dissemi- 
nated 


Pitch  black 
Brownish 
black 
Bluish  black 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


393 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 

Associates 

6. 
6.5 

Reddish  brown      C  —  Pinacoidal,    not      5.4     Fracture  surface  sometimes 
Blackish  brown             conspicuous               6.4        iridescent.     With     beryl, 

F — Conchoidal,  un- 
even 
Brittle 


tourmaline,  spodumene, 
cryolite.  Tantalum  pre- 
dominates in  tantalite,  and 
specific  gravity  may  be  as 
high  as  9. 


Pale  yellowish 
brown 
Gray 


C — Prismatic,  py- 
ramidal, not 
conspicuous 

F — Uneven 

Brittle 


4 . 2  Xot  as  heayy  as  cassiterite. 

4.3  Sometimes   in    fine   hair- 
like     inclusions.     Widely 
distributed.  With  quartz, 
feldspar,  hematite,  ilmen- 
ite,  chlorite,   apatite. 


Pale  brown 
Pale  yellow 
White 


C — Prismatic,     im- 
perfect 
F — Uneven 
Brittle 


6.8  Distinguished  by  high 
7 .  specific  gravity  and  hard- 
ness. In  veins  cutting 
granite,  gneiss;  also  in 
alluvial  deposits,  as  stream 
tin.  With  quartz,  wol- 
framite, scheelite,  arseno- 
pyrite,  molybdenite,  tour- 
maline, fluorite,  apatite. 


6.5 
7.6 


White 


C — Dodecahedral, 
indistinct 

F — Conchoidal,  un- 
even 

Brittle 


3.8  Andradite,  commonly  with 
4.2  magnetite,  epidote,  feld- 
spars, nephelite,  leucite ; 
almandite,  with  mica,  sta- 
urolite,  andalusite,  cyan- 
ite,  tourmaline. 


7. 
7.6 


White 
Gray 


C — None 

F — Conchoidal,  un- 
even 
Brittle 


2.9  Spherical  triangular  cross- 
3.2  section  and  hemimorphic 
development  important. 
In  pegmatites;  metamor- 
phic  rocks;  alluvial  de- 
posits. With  quartz,  feld- 
spar, cassiterite,  beryl, 
topaz,  fluorite. 


394 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak  —  White,  gray,  green,  red,  brown,  or  yellow 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CORUNDUM,  variety             Hexagonal                            Metallic            Dark  gray 
Emery         M  —  Fine  to  coarse  granu-  Dull                   Black 

A12O3  with  Fe3O4,  Fe2O3,  lar  Opaque 

SiO2 


228 


SPINEL,  varieties                    Cubic                                     Submetallic  Black 

Pleonaste    C — Octahedral,  well  de-  Dull  Brownish 

R2"(R'"O2)2        Hercynite          veloped,  common        Nearly  black 

R"  =  Mg,  Fe,    Gahnite       M — Compact,    granular,     opaque  Greenish 

Zn,  Mn     Picotite              disseminated  grains;  black 
R'"  =  Al,  Fe      Dysluite              sand 


267 


Streak— Black 


Molybdenite 
MoS2 


Hexagonal  Metallic  Bluish  lead 

C — Tabular,  rare  Opaque  gray 

M — Disseminated  grains, 
scales,  foliated 


205 


GRAPHITE         (Plumbago,   Hexagonal  Metallic 

black  lead)   C— Tabular,  rare  Dull 

C  M — Foliated,  scaly,  gran-  Opaque 

ular,  earthy 


Dark  steel 
gray 
Iron  black 


192 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


395 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 

Associates 

7.          Yellowish  brown    C  —  Indistinct                  3.7      Corundum      mixed      with 
9.          Blackish  brown      F  —  Uneven                      4  .  3        magnetite,  hematite, 
Brittle  to  tough                           quartz.     Resembles    iron 

ore,  powder  may  be  mag- 
netic. Properties  vary 
with*  composition.  With 
mica,  amphiboles,  chlor- 
ite, spinel;  in  crystalline 
limestones,  schists,  peri- 
dotite. 


7.6 
8. 


Grayish 
Grayish  green 
Pale  brown 
White 


C — Octahedral,  in- 
distinct 
F — Conchoidal 
Brittle 


3.6  Common  contact  mineral 
4.4  in  granular  limestones;  in 
igneous  rocks,  especially 
the  basic  olivine-bearing 
types;  rounded  grains  hi 
placers.  With  calcite, 
chondrodite,  serpentine, 
brucite,  olivine,  corun- 
dum, graphite,  pyroxenes. 


Hardness  1  to  3 


1.          Dark  lead  gray;  C — Basal,  perfect 
1.5         greenish  on  Sectile,  lamellae  are 

glazed        porce-      flexible 

lain     (graphite, 

shiny  black) 


4.7  Marks    paper.     Soft    and 

4.8  greasy  like  graphite,  but 
heavier    and    lighter 
colored.     In  granite  with 
cassiterite,       wolframite; 
also   in   crystalline  lime- 
stone. 


1.  Black,  shiny  C— Basal,  perfect  1 . 9 

2.  Dark  silver  gray    Sectile,  lamellae  are        2 . 3 

flexible 


Greasy  feel;  marks  paper; 
darker  than  molybdenite 
and  not  as  heavy.  In 
crystalline  limestone  with 
garnet,  spinel,  pyroxenes, 
amphiboles;  also  in  shale, 
gneiss,  and  mica  schist. 


396 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak— Black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

PYROLUSITE                          Orthorhombic  ?                   Metallic            Iron  black 
C  —  Often        pseudomor-  Dull                   Dark  steel 
MnO2                                             phous     after     man-  Opaque               gray 

227 


gamte 

M — Columnar,  fibrous, 
acicular,  often  di- 
vergent ;  dendritic ; 
powdery 


STIBNITE 

Sb2S3 

Orthorhombic                       Metallic 
C  —  Prismatic,     bent,  Opaque 
twisted,  common 
M  —  Fibrous,  b  1  a  d  e  d, 
columnar,     granular 

Dark  lead 
gray 
Black 

204 


Argentite  (Silver  glance) 
Ag2S 

Cubic                                     Metallic 
C  —  Octahedral,    cubical,  Opaque 
often  distorted 
M  —  Compact,      arbores- 
cent; coatings 

Dark  lead 
gray 
Black 

213 


GALENA  (Galenite) 
PbS 


Cubic 

C — Cubes  alone,  or  with 
octahedron,  well  de- 
veloped, common 

M — Granular,    cleavable 


Metallic 
Opaque 


Dark  lead 
gray 


212 

aggregates,  compact 

, 

CHALCOCITE 

Cu2S 

214 

Orthorhombic 
C  —  Tabular,   pseudohex- 
agonal,     deeply 
striated 
M  —  Granular,    compact, 
disseminated 

Metallic 
Opaque 

Dark  lead 
gray,      often 
tarnished 
dull  black, 
blue,  or  green 

Bournonite  (Cog-wheel  ore) 
Pb2Cu2Sb2S6 
217 

Orthorhombic 
C  —  Thick    tabular;    cog- 
wheel twins 
M  —  Compact,  granular 

Metallic 
Opaque 

Dark  steel 
gray 
Iron  black 

1.  DARK  GRAY  OR  BLACK  IN  COLOR 


397 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

1.           Black                     C  —  Indistinct                     4.7      Of  ten  soils  fingers.  Darker 
2.5       Bluish  black         Brittle                                 4.8       than    stibnite.     Withpsi- 
lomelane,    manganite, 
hematite,  limonite,  barite. 

2.          Dark  lead  gray 
2.6       Black 

C  —  Brachypina- 
coidal,   perfect, 
conspicuous, 
yielding  long, 
shiny  faces 
Slightly  sectile 

4  .  6      Tarnishes  black,  sometimes 
4  .  7        iridescent.     In  veins  with 
quartz,  -sphalerite,  galena, 
cinnabar,  barite,  gold. 

2.          Dark  lead  gray, 
2.5         shiny 

C  —  Indistinct 
F—  Hackly 
Perfectly  sectile 

7.2      Cuts  and  takes  impression 
7.4        like    lead,    hence    easily 
distinguished  from  other 
soft,  black  minerals.  With 
silver,  cobalt,  nickel  ores- 
proustite,        pyrargyrite, 
smaltite,  niccolite. 

2.5        Grayish  black 
Dark  lead  gray 

C  —  Cubic,   perfect, 
very    conspicu- 
ous 
Brittle 

7.3      Characterized  by  cleavage 
7.6        and  high  specific  gravity. 
Changes   to   cerussit£  or 
anglesite.     With  sphaler- 
ite,  pyrite,   chalcopyrite, 
calcite,  fluorite,  barite. 

2.6        Dark  gray,  shiny 
3.          Black,  shiny 

C  —  Indistinct 
F  —  Conchoidal 
Rather  brittle 

5  .  5      More   brittle   than   argen- 
5.8        tite.     Often  coated  with 
malachite    (green),    azur- 
ite  (blue).     With  chalco- 
pyrite,   bornite,    tetrahe- 
drite,  galena. 

2.5        Dark  gray 
3.          Black 

C  —  Imperfect 
F  —  Uneven 
Brittle 

5.7      Easily  recognized  by  cross 
5.9        or  cogwheel  appearance. 
With    galena,    sphalerite, 
tetrahedrite,  siderite.  stib- 
nite, chalcocite. 

398 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak— Black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Enargite 

Cii3AsS4 
219 


Orthorhombic  Metallic 

C — Prismatic,  small,  rare  Submetallic 

M — Compact,    granular,  Opaque 
columnar 


Grayish  black 
Iron  black 


Streak— Black 


TETRAHEDRITE 

Cubic                                     Metallic 

Dark  steel 

C  —  Tetrahedral,    often      Opaque 

gray 

Cu8Sb2S7 

highly  modified 

Iron  black 

M  —  Granular,  compact 

218 

Arsenic 

Hexagonal                            Metallic 

Dark  gray  to 

C  —  Rare                                Opaque 

black  on  ex- 

As 

M  —  Compact,  scaly,  fine 

posure,      tin 

granular,  with  reni- 

white  on 

form    or    botryoidal 

fresh  frac- 

194 

structure 

ture 

Uraninite  (Pitchblende) 

Cubic                                     Pitch-like 

Pitch  black 

C  —  Octahedral,  rare            Submetallic 

Brownish 

U03,  U02,  PbO,  etc. 

M  —  Botryoidal,     colum-  Dull 

black 

nar,  curved  lamellar,  Opaque 

Greenish 

granular,     compact, 

black 

apparently  a  m  o  r- 

262 

phous 

Ferberite 

Monoclinic                           Submetallic 

Iron  black 

C  —  Wedge  shaped,  short  Splendent 

Brownish 

FeW04 

prismatic,  tabular       Opaque 

black 

' 

M  —  Fan    shaped    aggre- 

gates, bladed,  granu- 

261 

lar,  compact 

WOLFRAMITE 

Monoclinic                           Submetallic 

Dark  gray 

C  —  Thick,  tabular,  short  Metallic 

Brownish 

(Fe,  Mn)WO4 

columnar,    often  Opaque 

black 

large 

Iron  black 

M  —  Bladed,    curved 

lamellar,      granular, 

261 

compact 

1.  DARK  GRAY  OR  BLACK  IN  COLOR 


399 


Hardness  1  to  3 

Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.          Grayish  black 


C — Prismatic,  per- 
fect, often  con- 
spicuous 

F — Uneven 

Brittle 


4.4  In  artificial  light  usually 
resembles  sphalerite.  In 
veins  with  other  copper 
minerals — chalcopyrite, 
bornite,  chalcocite. 


Hardness  over  3 

3.          Dark  gray               C  —  Indistinct                  4.3 
4.          Black                       F  —  Uneven                      5.4 
Brittle 

Characteristic  crystals- 
sometimes  coated  with 
chalcopyrite.  With  sphal- 
erite, galena,  bournonite, 
siderite,  malachite. 

3.          Dark  gray               C  —  Basal,  not  con-        5  .  6 
4.          Black                             spicuous                    5.8 
F  —  Uneven,    granu- 
lar 
Brittle 

Often  breaks  in  concentric 
or  onion-like  1  a  y.e  r  s. 
Color  and  streaks  darken 
on  exposure.  With  silver, 
cobalt,  nickel  ore  s  — 
proustite,  smaltite. 

3.          Brownish  black      F  —  Conchoidal,  un-        4  .  8 
5.5        Grayish  black               even                           9.7 
Brittle 

Pitch-like  appearance  and 
fracture  important.  Fresh 
material  is  hard  and 
heavy.  With  ores  of  lead, 
silver,  bismuth;  pyrite, 
orthite. 

5.          Brownish  black      C  —  Clinopinacoidal,       7  .  1 
5.5                                               perfect                        7.5 
F  —  Uneven 
Brittle 

In  granites  and  pegmatites. 
With  quartz,  chalcopy- 
rite, galena,  scheelite. 

5.          Brownish  black      C  —  Clinopinacoidal,       7  .  1 
5.5       Black                               perfect,       con-        7.5 

Structure,    cleavage,    and 
specific    gravity     impor- 

spicuous 
F — Uneven 
Brittle 


tant.  Powder  may  be 
slightly  magnetic.  With 
cassiterite,  quartz,  mica, 
fluorite,  apatite,  scheelite, 
molybdenite,  huebnerite. 


400 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak— Black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Psilomelane 

MnO2,  BaO,  H2O,  etc. 
253 


Amorphous?  Metallic  Iron  black 

M — Botryoidal,     r  e  n  i-  Dull  Bluish  black 

form,    stalactitic;  Opaque  Dark  gray 

smooth  surface 


Ilmenite  (Menaccanite) 
FeTiOs 


Hexagonal  Metallic  Iron  black 

C — Thick  tabular,  rhom-  Submetallic      Brownish 

bohedral  Opaque  black 

M — Thin  plates,  granu- 
lar, compact,  dis- 
seminated grains, 
pebbles,  sand 


MAGNETITE 

Fe(Fe02)2 


Cubic  Metallic 

C — Octahedrons,  dodeca-  Submetallic 

hedrons,  common        Dull 
M — Compact,    granular,   Opaque 
lamellar,       dissemi- 
nated, sand 


Iron  black 


268 


FRANKLINITE 

(Fe,Mn,Zn)(FeO2)2 
270 


Cubic  Metallic 

C — Octahedrons,  alone  or  Dull 

with   dodecahedron;  Opaque 

edges  often  rounded 
M — Compact,    granular, 

rounded  grains 


Iron  black 


COLUMBITE  (Tantalite)        Orthorhombic  Submetallic       Iron  black 

C — Short  prismatic,  tab-  Greasy  Brownish 

ular  Dull  black 

(Fe,Mn)[(Nb,Ta)O3]2  M — Compact,      dissemi-  Opaque 

nated 


273 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


401 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

5.          Black                       F  —  Conchoidal,  un-        3.7      Often     with     fine,     sooty 
6.          Brownish  black            even                           4.7        coating      of      pyrolusite. 
Brittle                                            With     other     manganese 
minerals;  limonite,  barite. 

Black 
Brownish  black 


C — None,   partings 

may  be  noted 
F — Conchoidal 
Brittle 


4.5  Sometimes  slightly  mag- 
5.5  netic  but  not  as  strongly 
as  magnetite.  With  hema- 
tite, magnetite,  apatite, 
serpentine,  titanite,  ru- 
tile.  Common  in  black 
sands. 


5.6 
6.5 


Black 


C — Indistinct,  oc- 
tahedral part- 
ing 

F — Conchoidal,  un- 
even 

Brittle 


4.9      Very    strongly    magnetic. 

5.2  Crystals  usually  perfect 
and  with  bright  surfaces. 
Independent  deposits ;  dis- 
seminated; black  sands. 
With  chlorite,  horn- 
blende, pyroxene,  feld- 
spar, quartz,  pyrite,  chal- 
copyrite,  epidote. 


5.5 
6.5 


Black 
Brownish  black 


C — Octahedral,  in- 
distinct 
F — Conchoidal 
Brittle 


5 .  Powder  frequently  slightly 
5.2  magnetic.  Distinguished 
by  associates — will  emit  e 
(yellow  or  green),  zincite 
(red) ,  rhodonite  (flesh 
red),  calcite. 


6. 
6.5 


Black 

Brownish  black 
Grayish  black 


C — Pinacoidal,  not 
conspicuous 

F — Conchoidal,  un- 
even 

Brittle 


5 . 4  Fracture  surf ac  e  sometimes 
6.4  iridescent.  With  beryl, 
tourmaline,  spodumene, 
cryolite.  Tantalum  pre- 
dominates in  tantalite  and 
specific  gravity  may  be  as 
high  as  9. 


402 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak  —  Black 

Crystallization 

Name,  Composition,  and 

Structure 

Luster 

Color 

Reference 

Crystals  =  C 

Transparency 

Massive  =  M 

CORUNDUM,  variety 

Hexagonal 

Metallic 

Dark  gray 

Emery  Always  massive,  fine  to    Dull 

Black 

A12O3,  with  Fe3O4,  Fe2Oc 

,           coarse  granular 

Opaque 

SiO2 

228 

A.     MINERALS  WITH  METALLIC  LUSTER 

Streak  —  Metallic  white  or  steel  gray 

Bismuth 

Hexagonal 

Metallic 

Silver  white, 

C—  Rare 

Opaque 

with  reddish 

Bi 

M  —  Reticulated,  a  r  b  o- 

tinge 

rescent,  platy 

195 

SILVER 

Cubic 

Metallic 

Silver     white, 

C  —  Small,  often  distorted     Opaque 

tarnishing 

Ag 

M  —  Grains,  scales,  plates, 

yellow, 

twisted  hair-  or  wire- 

brown,  or 

like  forms,  lumps 

black 

199 

PLATINUM 

Cubic 

Metallic 

Tin  white 

C  —  Small,  rare 

Opaque 

Steel  gray 

Pt 

M  —  Scales,   grains,  nug- 

gets 

195 

Streak  —  Black 

Molybdenite 

Hexagonal 

Metallic 

Bluish  lead 

C  —  Tabular,  rare 

Opaque 

gray 

MoS2 

M  —  Disseminated  grains, 

scales,  foliated 


205 


1.    DARK  GRAY  OR  BLACK  IN  COLOR 


403 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

7.          Black                       C  —  Indistinct                  3.7      Corundum  mixed  with  iron 

9.          Brownish  black     F  —  Uneven                      4.3        ore.     May  be  magnetic. 

Brittle  to  tough                          With  mica,    amphiboles, 

chlorite,  spinel;  in  crystal- 

line    limestone,     schist, 

peridotite. 

2.  METALLIC  WHITE  OR  LIGHT  METALLIC  GRAY  IN  COLOR 


Hardness  1  to  6 


2.         Lead  gray,  shiny 

C  —  Basal,    perfect, 

9  .  7      Often  shows  brassy  tarnish 

2.5 

usually  conspic- 

9.8       colors.     With  silver,   co- 

uous. 

balt,    nickel,    tin    ores  — 

Sectile 

smaltite,  niccolite,  cassit- 

erite  ;     wolframite. 

2.5        Silver  white, 

C  —  None 

10  .         Color  and  streak  darken  on 

3.           shiny 

F—  Hackly 

12.          exposure.       With  silver, 

Light  lead  gray, 

Malleable,  ductile 

lead,       arsenic,       cobalt, 

shiny 

nickel       ores  —  argentite, 

pyrargyrite,        proustite, 

galena,  smaltite;  fluorite, 

calcite,  barite. 

4.         Light  steel  gray, 

C  —  None 

14.        Heavier   than   silver   and 

6.           shiny 

F—  Hackly 

19.          does   not   tarnish.     May 

Malleable,  ductile 

be  magnetic  if  much  iron 

be  present.     With  chrom- 

ite,  magnetite,   gold. 

Hardness  1  to  3 


1.          Dark  lead  gray,  C — Basal,  perfect 

1.6          greenishon  Sectile,  lamellae 

glazed  p  o  r  c  e-  flexible 

lain     (graphite, 

shiny  black) 


4.7  Marks    paper.     Soft    and 

4.8  greasy  like    graphite  but 
heavier        and        lighter 
colored.     In  granite  with 
cassiterite,  wolf ramite  ;•  in 
crystalline  limestone. 


401 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — Black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

STIBNITE 

Sb2S3 

204 


Orthorhombic  Metallic 

C — Prismatic,  bent,  Opaque 

twisted,  common 
M — Fibrous,  bladed,  co- 
lumnar,      granular, 
compact 


Light  lead 
gray 


GALENA  (Galenite) 
PbS 

212 


Cubic  Metallic 

C — Cubes,  alone  or  with  Opaque 

octahedron,    c  o  m- 

mon,  well  developed 
M — Granular,    cleavable 

aggregates 


Lead  gray 


Streak—  Black 

Arsenic 
As 

194 

Hexagonal                             Metallic 
C  —  Rare                                 Opaque 
M  —  Compact,  scaly,  fine 
grained,      reniform, 
botryoidal 

Tin  white,  on 
fresh       frac- 
ture 

Cobaltite 

CoAsS 

210 

Cubic                                     Metallic 
C  —  Cubes,  pyritohedrons,  Opaque 
small,  well  developed 
M  —  Granular,  compact 

Silver  white 
Steel  gray,  at 
times  with 
reddish 
tinge 

Smaltite 
CoAs2 

Cubic                                     Metallic 
C  —  Rare                                Opaque 
M  —  Granular,  compact 

Tin  white 
Light  steel 
gray 

210 


ARSENOPYRITE 

FeAsS 

211 


Orthorhombic  Metallic 

C — Prismatic,  common      Opaque 
M — Compact,    granular, 
columnar,  radial 


Tin  white 
Light  steel 
gray,  tar- 
nishes yel- 
low 


2.    METALLIC  WHITE  OR  LIGHT  METALLIC  GRAY  IN  COLOR      405 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture    =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

2. 
2.5 

Dark  lead  gray 
Black 

C  —  Brachypina- 
coidal,    perfect, 

4.6 
4.7 

Differs     from,     galena    in 
cleavage  and  specific  grav- 

conspicuous, 
yielding      long 
shiny  faces 
Slightly  sectile 


ity.  Tarnishes  black, 
sometimes  iridescent.  In 
veins  with  quartz,  sphal- 
erite, galena,  cinnabar, 
barite,  gold. 


2.6 


Dark  lead  gray 
Grayish  black 


C — Cubic,  perfect, 
very  conspicu- 
ous 

Brittle. 


7.3  Characterized  by  cleavage 
7 . 6  and  high  specific  gravity. 
Changes  to  cerussite, 
pyromorphite,  or  angle- 
site.  With  sphalerite, 
pyrite,  chalcopyrite,  cal- 
cite,  fluorite,  barite. 


Hardness  over  3 


3.         Lead  gray               C  —  Basal,  not  con-        5  .  6 
4.          Grayish  black               spicuous                    5  .  8 
F  —  Uneven,  granular 
Brittle 

Often  breaks  in  concentric 
or  onion-like  layers. 
Color  and  streak  darken 
on  exposure.  With  silver, 
cobalt,  nickel  ore  s  — 
proustite,  smaltite. 

6.5        Dark  grayish          C  —  Cubic,  not  con-        6  . 
black                            spicuous                    6.4 
F  —  Uneven 
Brittle 

May  show  red  tarnish. 
Often  with  pink  coating 
of  erythrite  (cobalt 
bloom).  With  native 
silver,  smaltite,  niccolite, 
pyrrhotite,  chalcopyrite. 

6.6        Grayish  black        C  —  Indistinct                  6  .  4 
F  —  Uneven                      6  .  6 
Brittle 

May  have  dull  tarnish  and 
pink  coating  of  erythrite. 
With  niccolite,  cobaltite, 
native  bismuth  and  silver, 
proustite,  barite,  fluorite, 
calcite. 

5.5        Dark  grayish          C  —  Prismatic,    not        5.9 
6.           black                            conspicuous              6.2 
F  —  Uneven 
Brittle 

Whiter  than  marcasite- 
More  common  than 
smaltite.  With  chalcopy- 
rite, pyrite,  sphalerite,cas- 
siterite,  smaltite,  native 
gold  and  silver,  serpentine. 

406 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak— Black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

MARCASITE  (White    iron    Orthorhombic                      Metallic  Steel  gray 

pyrites)   C — Tabular,  often               Opaque  Pale  brass  yel- 

FeS2                                                twinned,  resembling  low,   more 

cock's  combs  brassy  on  ex- 

M — Compact,  stalactitic,  posure 
211                                              globular,  radiated 

A.     MINERALS  WITH  METALLIC  LUSTER 
Streak — Brown  or  yellow 


LIMONITE,  varieties  M — Earthy,  porous,  Earthy  Yellow 

Yellow  ocher          clay-like  Dull  Brownish 

Fe2O3.H2O      Bog  iron  ore  Opaque  yellow 

235 


GOLD 

Au 


Cubic  Metallic 

C — Small,  often  distorted  Opaque 
M — Grains,  scales,  nug- 
gets, dust 


Golden  yellow 
Brassy  yellow 
Light  yellow 


200 


Streak— Black 


CHALCOPYRITE 

CuFeSa 

215 


Tetragonal  Metallic 

C — Bisphenoids,     resem-  Opaque 

bling     tetrahedrons, 

common 
M — Compact 


Brass  yellow 
Golden  yellow 


MARCASITE  (White  iron       Orthorhombic  Metallic 

pyrites)        C — Tabular,  often 

twinned,  resembling  Opaque 


FeSs 


cock's  combs 
M — Compact,  stalactitic, 
globular,  radiated 


Pale  brass  yel- 
low, more 
brassy  on  ex- 
posure 


211 


2.     METALLIC  WHITE  OR  LIGHT  METALLIC  GRAY  IN  COLOR     407 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.          Dark  greenish        C  —  Indistinct                  4.6      Alters  to  limonite,  melan- 
6.5         black                     F—  Uneven                      4.8        terite.     With    other   sul- 
Brittle                                           phides  —  galena,    sphaler- 
ite, chalcopyrite,  pyrite; 
calcite,  dolomite. 

3.  YELLOW  IN  COLOR 


Hardness  1  to  6 


1.         Yellowish               C—  None 
4.           brown                   F  —  Earthy 
Brittle 

3.4      Yellow  ocher,  earthy,  may 
4.          have   greasy   feel,    when 
impure   gritty;   bog   iron 
ore,  porous. 

2.5       Golden  yellow       C  —  None 
3.                                        F—  Hackly 
Malleable,  ductile 

« 

15.6      Does  not  tarnish.     Char- 
19  .  3        acterized  by  streak,  speci- 
fic gravity,  and  tenacity 
Frequently      in      quartz 
veins;  placers.  Common- 
ly with  pyrite,  and  other 
sulphides. 

Hardness  over  3 


3.5      Greenish  black       C — Indistinct  4.1      Softer,  and  deeper  yellow 

4.  F — Uneven  4.3        than  pyrite.    Frequently 

Brittle  with  iridescent   tarnish. 

With  pyrite,  bornite,  ga- 
lena, sphalerite,  tetrahe- 
drite,  chalcocite. 

6.          Dark  greenish        C — Indistinct  4 . 6      Distinguished  from  pyrite 

6.5         black  F — Uneven  4.8       by     crystallization     and 

Brownish  black      Brittle  lighter     color     on    fresh 

fracture.  Alters  more 
readily  than  pyrite,  form- 
ing limonite,  melanterite. 
Occurrence  same  as 
pyrite,  less  abundant. 


408 


A.      MINERALT  WITH  METALLIC  LUSTER 


Streak—Black 


Name,  Composition,  and 
Reference 

'Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

PYRITE  (Iron  pyrites, 

fool's  gold) 
FeS2 


208 


Cubic  Metallic 

C — Cubes,    octahedrons,   Opaque 
pyritohedrons,  com- 
mon, often  striated 
M — Compact,  fine  gran- 
ular ;  botryoidal,  stal- 
actitic 


Brass  yellow 
Golden  yellow 
with     varie- 
gated      tar- 
nish 


A.  MINERALS  WITH  METALLIC  LUSTER 


200 


Streak — Gray,  red,  or  yellow 


Bismuth 

Hexagonal                            Metallic 

Light  copper 

C  —  Rare                                Opaque 

red 

Bi 

M  —  Reticulated,      arbo- 

rescent, platy 

196 

• 

COPPER 

Cubic                                     Metallic 

Copper  red, 

C  —  Cubes,    octahedrons,  Opaque 

tarnishing 

Cu 

tetrahexahedrons 

readily  red, 

M  —  Scales,  plates,  lumps, 

blue,  green, 

arborescent  aggre- 

black 

196 

gates 

GOLD 

Cubic                                     Metallic 

Golden  yellow 

C  —  Small,  distorted,  rare  Opaque 

Brassy  yellow 

Au 

M  —  Grains,  scales,  dust, 

Light  yellow 

nuggets 

Streak— Black 


BORNITE 


x  =  6,  10,  12 
216 


Cubic  Metallic 

C — Rare  Opaque 

M — Compact,  granular 


Bronze  brown 
Copper      red, 
on  fresh  frac- 
ture 


3.     YELLOW  IN  COLOR 


409 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.          Greenish  black       C  —  Indistinct                  4  .  9      Harder  than  chalcopyrite 
6.5        Brownish  black      F  —  Uneven                      5.2        Alters  to  limonite.  Wide- 
Brittle                                           ly  distributed  in  all  types 

of 'rocks.  With  other  sul- 
phides— galena,  sphaler- 
ite, chalcopyrite;  quartz. 


4.  BRASS,  BRONZE,  OR  COPPER  RED  IN  COLOR 


Hardness  1  to  3 


2.          Lead  gray,  shiny   C  —  Basal,    perfect, 
2.6                                              usually  conspic- 
uous 
Sectile 

9.7      Often  shows  brassy  tarn- 
9  .  8       ish.     Frequently  with  sil- 
ver,   cobalt,    nickel,    tin 
ore  —  smaltite,      niccolite, 
cassiterite,  wolframite. 

2.5        Copper  red,            C  —  None 
3.            shiny                     F  —  Hackly 
Ductile,  malleable 

8  .  5      Cementing  material  in  con- 
9.          glomerate  or  filling  cavi- 
ties in  trap  rocks.    With 
cuprite,malachite,azurite, 
native  silver,  melaconite, 
epidote,  datolite,  zeolites. 

2.5        Golden  yellow        C  —  None 
3.                                         F—  Hackly 
Malleable,  ductile 

15.6    Does  not  tarnish.    Charac- 
19.3       terized  by  streak,  specific 
gravity,     and     tenacity. 
Frequently     in      quartz 
veins;  placers.  Common- 
ly with  pyrite  and  other 
sulphides. 

Hardness  over  3 


3.          Grayish  black        C — Indistinct  4 . 9      Usually  with  peacock  tarn- 

3.5  F — Uneven  5.2        ish  colors  (purple  copper 

Brittle  ore).     With  chalcopyrite, 

chalcocite,         malachite, 
cassiterite,  siderite. 


410 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak— Black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CHALCOPYRITE 

CuFeS2 

215 


Tetragonal  Metallic 

C — Bisphenoids,     resem-  Opaque 

bling     tetrahedrons, 

common 
M — Compact,  granular 


Brass  yellow 
Golden  yellow 


PYRRHOTITE 

FeS 


Hexagonal  Metallic 

C — Tabular,  rare  Opaque 

M — Compact,  granular 


Bronze  yellow 
Bronze  brown 


207 


Niccolite 
NiAs 


Hexagonal  Metallic 

C — Rare  Opaque 

M — Compact,     dissemi- 
nated 


Light  copper 
red 


208 


MARCASITE  (White    iron    Orthor'iombic 

pyrites)  C — Tabular,  often 
FeS2  twinned  resembling 

cock's  combs 
M — Compact,  stalactitic, 
globular,  radiated 


Metallic 
Opaque 


Steel  gray 

Pale  brass 
yellow,  more 
brassy  on  ex- 
posure 


211 


PYRITE  (Iron  pyrites, 

fool'sgold) 
FeS, 


Cubic  Metallic  Brass  yellow 

C — Cubes,    octahedrons,  Opaque  Golden       yel- 

pyritohedrons,   very  low,     with 

common,  often  stri-  variegated 

ated  tarnish 

M — Compact,  fine  gran- 
ular; botryoidal, 
stalactitic 


208 


4.  BRASS,  BRONZE,  OR  COPPER  RED  IN  COLOR 


411 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.6       Greenish  black       C—  Indistinct                 4.1      Softer,  and  deeper  yellow 

4.                                        F  —  Uneven                     4.3       in  color  than  pyrite.    Fre- 

Brittle                                           quently    with    iridescent 

tarnish.        With    pyrite, 

bornite,   galena,   sphaler- 

ite, tetrahedrite,  chalco- 

3.5        Dark  grayish          C  —  Basal,  not  con- 
4.6         black                           spicuous 
F  —  Uneven 
Brittle 

4.5      Powder      frequently      at- 
4  .  6        tracted  by  magnet.     Sub- 
ject to  dark  brown  tarn- 
ish.      In   basic    igneous 
rocks.  With  chalcopyrite, 
pyrite,   galena. 

6.5        Dark  brownish      C  —  Indistinct 
black                    F  —  Uneven 
Brittle 

7.3      Often  with  green  coating 
7.7       of      annabergite     (nickel 
bloom).        With    cobalt, 
nickel,   silver  minerals  — 
smaltite,  proustite,  native 
silver  ;     native    bismuth 
and  arsenic  ;  calcite. 

6.          Dark  greenish        C  —  Indistinct 
6.5           black                  F  —  Uneven 
Brittle 

4.6      Distinguished  from  pyrite 
4.8       by    crystallization     and 
lighter     color     on     fresh 
fracture.        Alters    more 
readily  than  pyrite,  form- 
ing limonite,  melanterite. 
'  Occurrence  same   as  for 
pyrite,  but  not  as  abun- 
dant. 

6.          Greenish  black       C  —  Indistinct 
6.5        Brownish  black      F  —  Uneven 
Brittle 

4.9      Alters  to  limonite.  Widely 
5  .  2        distributed  in  all  types  of 
rocks.    With    other     sul- 
phides —  galena,  sphaler- 
ite, chalcopyrite.;  quartz. 

412 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

LIMONITE,  varieties  C — Unknown                       Dull                   Yellowish 

Brown  ocher  M — Compact,  earthy,        Earthy                 brown 

Fe2Os.H2O       Bog  iron  ore  porous,  pisolitic,          Opaque             Dark  brown 

Brown  clay  oolitic 
ironstone 

235 

HEMATITE,  varieties  Hexagonal                            Dull                   Brownish 

Red  ocher  M — Fine    granular,  Earthy              Cherry  red 

Fe2O3               Oolitic  earthy,  scaly,  oolitic,  Opaque 

Fossiliferous  fossiliferous 
230 


CINNABAR 
HgS 

215 


Hexagonal  Adamantine     Scarlet  red 

C — Rhombohedral,  thick  Dull  .       Brownish  red 

tabular,  small,  rare     Transparent 
M — Fine     granular,     fi-     to  opaque 

brous,  disseminated, 

earthy  coating 


Proustite 

AgsAsSs 


Hexagonal  Adamantine     Scarlet 

C — Small,  complex,  rare  Dull  Vermilion 

M — Disseminated,  Transparent 

crusts,  bands  to  translucent 


217 


Pyrargyrite 
AgsSbSs 

217 


Hexagonal  Adamantine 

C — Small,  complex,  rare  Metallic 

M — Disseminated,  Transparent 
crusts,  bands  to  opaque 


Dark  red 


COPPER 

Cu 


Cubic  Metallic  Copper  red, 

C — Cubes,    octahedrons,  Opaque  tarnishing 

tetrahexahedrons  readily  to 

M — Scales,  plates,  lumps,  red,  blue, 

arborescent  aggre-  green,  black 

gates 


196 


5.  RED,  BROWN,  OR  BLUE  IN  COLOR 


413 


Hardness  1  to  3 

Hard- 
Stre 
ness 

Cleavage  =  C 
ak                  Fracture  =  F 
Tenacity 

eific          Characteristics  and 
vity                 Associates 

1.          Yellowish                C  —  None                          3.4      Brown  ocher,  earthy,  may 
3.           brown                    F  —  Earthy                      4.          soil  fingers;  bog  iron  ore, 
Brittle                                           porous;  brown  day  iron- 
stone,   massive    or    con- 
cretionary,  impure  from 
clay,  sand. 

1.          Cherry  red              C  —  None                         4.9      Red  ocher,  earthy;  oolitic, 
3.          Reddish  brown      F  —  Earthy                       5  .  3        fish-egg  structure  ;  fossil- 
Brittle                                           iferous,     replacement    of 
shells. 

2.          Scarlet 
2.6        Reddish 

C  —  Prismatic,    not        8  .         Color,  streak,  high  specific 
brown             conspicuous              8.2        gravity    important;    the 
F  —  Uneven                                  latter   often   reduced  by 
Brittle  to  sectile                          gangue.    Disseminated  in 
silicious  rocks,  with  native 
mercury,   pyrite,   marca- 
site,  realgar,  stibnite. 

2.6        Scarlet                     C  —  Indistinct                  5.5      Termed  light  ruby  silver 
Aurora  red              F  —  Conchoidal               5  .  6        ore.     Distinguished  from 
Brittle                                           cinnabar    by    associates. 
With  pyrargyrite,  in  veins 
with  other  silver  minerals 
and  galena. 

2.6        Cherry  red              C  —  Indistinct                  5  .  8      Frequently  as  gray  or  dark 
3.          Purplish  red           F  —  Conchoidal                            red    bands,     dark    ruby 
Brittle                                         silver  ore.    With  proust- 
ite,  in  veins  with  other  sil- 
ver minerals  and  galena. 

2.6        Copper  red,            C  —  None                         8.5      Cementing  material  in  con- 
3.            shiny                     F  —  Hackly                      9  .          glomerate,  or  filling  cavi- 
Ductile,  malleable                      ties  hi  trap  rocks.     With 

euprite,malachite,azuTite, 
native  silver,  melaconite, 
epidote,  datolite,  zeo- 
lites, quartz,  calcite. 


414 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

LIMONITE,  varieties 

Compact 

Fe2O3.H2O       Bog  iron  ore 
Brown  clay 
ironstone 


C — Always    p  s  e  u  d  o-  Metallic 
morphs,     commonly  Dull 
after  pyrite,  marca-  Opaque 
site,  siderite 

M — Compact,  stalactitic, 
botryoidal,  nodular; 
often  with  internal 
radial  fibrous  struc- 
ture; porous 


Yellowish 
brown 
Dark  brown 


235 

Uraninite  (Pitchblende)           Cubic                                    Submetallic 
C  —  Octahedral,  rare           Dull 
UO3,  UO2,  PbO,  etc.            M—  Botryoidal,     colum-  Opaque 
nar,  curved  lamellar, 
granular,     compact; 
apparently       amor- 
phous 
262 

Brown 

Blackish 
brown 

HEMATITE,  varieties             Hexagonal                            Submetallic 
Argillaceous  M  —  Compact,    granular,  Dull 
Fe2O3               Compact                 columnar,  splintery,  Opaque 
radiated,      reniform 
and  botryoidal 

Brownish  red 
Dark  red 
Blackish  red 

235 


SIDERITE 
FeCO, 


Hexagonal  Dull 

C — Rhombohedral,     Vitreous 
curved    or    saddle-  Translucent 
shaped,  common  to  opaque 

M — Cleavable,  granular, 
compact,  botryoidal 


Dark  brown 
Reddish 
brown 


248 


SPHALERITE 

ZnS 

206 


Cubic  Submetallic  Brown 

C — Tetrahedral,  common  Resinous  Yellowish 

M — Cleavable,  fine  and  Opaque  to  brown 

coarse  grained  aggre-    translucent  Reddish 

gates,  compact  brown 


6.  RED,  BROWN,  OR  BLUE  IN  COLOR 


4'15 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.          Yellowish  brown   F  —  Conchoidal;  un-        3  .  4      Often  with  black,  varnish- 
6.5                                              even,  earthy             4.          like  surface,  passing  into 
Brittle                                           soft,  yellow  ocherous  var- 

iety.  Compact  Hmonite, 
massive,  with  fibrous 
structure,  rather  pure; 
brown  day  ironstone  mass- 
ive or  concretionary,  im- 
pure from  clay,  sand;  bog 
iron  ore,  porous. 


3. 

Dark  brown 

F  —  Conchoidal,  un- 

4.8 

Structure  and  fracture  im- 

5.5 

Olive  green 

even 

9.7 

portant.     Fresh  material 

Grayish 

Brittle 

is  hard  and  heavy.     With 

ores  of  lead,  silver,  bis- 

muth; also  orthite. 

3. 
6. 

Cherry  red 
Reddish  brown 

C  —  None,     parting 
sometimes 
noted 
F  —  Uneven,  splint- 
ery 
Brittle 

4.9      Argillaceous   hematite,   im- 
5.3        pure    from    clay,     sand, 
jasper;  compact  hematite, 
usually  quite  pure. 

3.5 

4. 


Yellowish  brown 
Pale  yellow 


C — Rhombohedral, 
perfect,  con- 
spicuous 

F — Conchoidal 

Brittle 


3.7  Curved  crystals,  cleavage, 
3.9  and  rather  high  specific 
gravity  characteristic.  In 
ore  deposits;  beds  and 
concretions  in  limestone 
and  shale.  With  pyrite, 
chalcopyrite,  galena,  tet- 
rahedrite,  cryolite. 


3.5       Light  brown 
4.         Pale  yellow 


C — Dodecahedral, 
perfect,  con 
spicuous 

F — Conchoidal 

Brittle 


3 . 9  Color  and  streak  vary  with 
4.2  impurities.  Extensively 
in  limes  tone.  With 
galena,  chalcopyrite,  py- 
rite, barite,  fluorite,  sider- 
ite,  rhodochrosite. 


416 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CUPRITE 
Cu2O 


232 


Cubic  Adamantine      Cochineal  red 

C — Octahedrons,  dodeca-  Dull  Brick  red 

hedrons,  alone  or  in  Translucent      Dark  red 
combination  to  opaque 

M — Compact,  granular, 
earthy ;  slender  crys- 
tal aggregates  (chal- 
cotrichile) 


Zincite 
ZnO 


Hexagonal  Subadaman-     Dark  red 

C — Hemimorphic,  rare         tine  Blood  red 

M — Compact,    granular,  Vitreous 
foliated  Translucent 

to  opaque 


228 


Huebnerite 
MnWO4 

260 


Monoclinic  Submetallic      Reddish 

C — Long,  fibrous,  bladed,  Resinous  brown 

stalky,   often  diver-  Opaque  to         Brown 

gent,    without  good     translucent 

terminations 
M — Compact,    lamellar, 

granular 


WOLFRAMITE 

(Fe,Mn)WO4 

261 


Monoclinic 


Submetallic       Reddish 


C — Thick,  tabular,  short  Opaque 
columnar,  often  large 

M — Bladed,  curved  lam- 
ellar, granular,  com- 
pact 


brown 
Dark  brown 


Ferberite 
FeWO4   - 

261 


Monoclinic  Submetallic 

C — Wedge  shaped,  short  Opaque 

prismatic,  tabular 
M — Fan    shaped   aggre- 
gates, bladed,  granu- 
lar, compact 


Brown 
Blackish 
brown 


5.  RED,  BROWN,  OR  BLUE  IN  COLOR 


417 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.6        Brownish  red          C  —  Indistinct                  5.7      Characterized     by      asso- 
4.          Dirty  brown           F  —  Uneven                      6  .  1        ciates,  copper  minerals  — 
Brittle                                           malachite  (green)  azurite 

(blue),  chalcocite  and 
melaconite  (black),  chal- 
copyrite  (yellow),  native 
copper. 


4. 
4.6 


Reddish  yellow 
Orange  yellow 


C — Basal,  perfect, 
usually  c  o  n- 
spicuous 

F — Uneven 

Brittle 


5 . 4  Distinguished  by  associates 
5.7  — calcite,  franklinite 
(black),  willemite  (yellow 
to  green),  rhodonite  (flesh 
red).  On  exposure  be- 
comes coated  with  the 
white  carbonate. 


4.6        Yellowish  brown    C — Clinopinacoidal, 
6.6        Greenish  gray  perfect,    c  o  n- 

spicuous 
Brittle 


6.7  Structure,  cleavage,  spe- 
7.3  cine  gravity  important. 
In  quartz  veins.  With 
fluorite,  pyrite,  scheelite, 
wolframite,  galena,  tetra- 
hedrite. 


6. 
6.6 


Dark  red  brown 


C — Clinopinacoidal, 
perfect,  c  o  n- 
spicuous 

F — Uneven 

Brittle 


7.1  Distinguished  from  hueb- 
7.5  nerite  by  streak.  Pow- 
der may  be  slightly  mag- 
netic. With  cassiterite, 
quartz,  mica,  fluorite, 
apatite,  scheelite,  molyb- 
denite, huebnerite. 


6. 
6.6 


Brown 
Dark  brown 


C — Clinopinacoidal, 

perfect. 
F — Uneven 
Brittle 


7.5      In  granites  and  pegmatites. 
With     quartz,     chalcopy- 
rite,  galena,  scheelite. 


418 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak — White,  gray,  green,  red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

RUTILE 

TiO2  or  TiTiO4 

224 


Tetragonal  Metallic  Reddish 

C — Prismatic,    vertically  Adamantine       brown 
striated;      twinned,  Opaque  to        Dark  red 
yielding  knee-shaped     transparent 
or  rosette  forms 
M — Compact,      dissemi- 
nated 


CASSITERITE,  varieties        Tetragonal 


Adamantine     Reddish 


Ordinary     C — Thick  prismatic,  Resinous 
SnO2  or  Wood  tin  knee-shaped    twins,  Dull 

SnSnC>4  Stream  tin          common  Translucent 

M — Compact;  reniform,  to  opaque 
botryoidal,  rounded 
pebbles,  often  with 
internal,  radial  fib- 
rous structure,  wood 
226  tin 


brown 
Yellowish 

brown 
Dark  brown 


5.  RED,  BROWN,  OR  BLUE  IN  COLOR 


419 


Hardness  over  6 

Hard- 
ness 

Streak 

Cleavage  =  C        ~ 
Fracture  =  F 
Tenacity 

cific          Characteristics  and 
vity                 Associates 

6. 
7. 

Pale  yellowish 
brown 
Gray 

C  —  Prismatic,    py-        4  .  2      Not  as  heavy  as  cassiterite- 
ramidal,    not         4.3        Often  in  fine,  hair-like  in- 
conspicuous                          elusions.     Widely    distri- 
F  —  Uneven                                  buted.    With  quartz,  f  eld- 
Brittle                                           spar,     ilmenite,     chlorite, 
apatite. 

6. 
7. 

Pale  yellow 
Pale  brown 
White 

C  —  Indistinct                  6.8      Distinguished  by  high  spe- 
F  —  Uneven                      7.          cific    gravity.     In    veins 
Brittle                                           cutting  granite,  gneiss;  in 

alluvial  deposits,  as  stream 
tin.  With  quartz,  mica, 
wolframite,  scheelite,  ar- 
senopyrite,  molybdenite, 
tourmaline,  fluorite,  apat- 
ite, chlorite. 


420 


A.  MINERALS  WITH  METALLIC  LUSTER 


Streak— Black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

BORNITE  (Purple    copper     Cubic  Metallic 

CuxFe2Sx  ore)      C — Rare  Opaque 

M — Compact,  granular 
x  =  6,  10,  12 
216 


Bronze  brown 
Copper  red 

tarnishes 

readily 


Uraninite  (Pitchblende) 
UO3,  UO2,  PbO,  etc. 

262 


Cubic 


Submetallic       Brown 


C — Octahedral,  rare  Dull 

M — Botryoidal,     colum-  Opaque 
nar,  curved  lamellar, 
granular      compact, 
apparently       amor- 
phous 


Blackish 
brown 


PYRRHOTITE 

FeS 


Hexagonal  Metallic  Bronze  brown 

C — Tabular,  rare  Opaque  Bronze  yellow 

M — Compact,  granular 


207 


WOLFRAMITE 
(Fe,Mn)WO4 

261 


Monoclinic 


Submetallic       Grayish 


C — Thick  tabular,  short  Opaque 
columnar,  often 
large 

M — Bladed,  curved  lam- 
ellar, granular 


brown 
Dark  brown 


Niccolite 

NiAs 


Hexagonal  Metallic 

C — Rare  Opaque 

M — Compact,      dissemi- 
nated 


Light  copper 
red 


208 


5.  RED,  BROWN,  OR  BLUE  IN  COLOR 


421 


Hardness  1  to  6 


Hard-            gtp 
ness 

Cleavage  =  C           ~ 
eak                 Fracture   =  F           ^ 
Tenacity 

3ific           Characteristics  and 
vity                 Associates 

3.          Grayish  black        C  —  Indistinct                  4  .  9      Usually  with  peacock  tarn- 
F  —  Uneven                      5.2        ish  colors  —  purple  copper 
Brittle                                           ore.     With    chalcopyrite, 
chalcocite,  malachite,  cas- 
siterite,  siderite. 

3.          Brownish  black      F  —  Conchoidal,  un-        4  .  8      Structure  and  fracture  im- 
6.6        Grayish  black               even                           9.7       portant.     Fresh  material 
Brittle                                         is  hard  and  heavy.     With 
ores  of  lead,   silver,  bis- 
muth ;  also  pyrite,  orthite. 

3.5 
4.6 


Dark  grayish 
black 


C — Basal,  not  con- 
spicuous 
F — Uneven 
Brittle 


4.5  Powder      frequently      at- 

4 . 6  tracted  by  magnet.     Sub- 
ject to  dark  brown  tarn- 
ish.       In    basic    igneous 
rocks.  With  chalcopyrite, 
pyrite,  galena. 


6.6 


Black 
Brownish  black 


C — Clinopinacoidal, 
perfect,  c  o  n- 
spicuous 

F — Uneven 

Brittle 


7 . 1  Structure,  cleavage,  spe- 
7.5  cific  gravity  important. 
Powder  may  be  slightly 
magnetic.  With  cassiter- 
ite,  quartz,  mica,  fluorite, 
apatite,  scheelite,  molyb- 
denite, huebnerite. 


6.6        Dark  brownish       C — Indistinct  7 . 3      Often    with    green    crust 

black  F — Uneven  7.7        of     annabergite      (nickel 

Brittle  »  bloom).        With    cobalt, 

nickel,  silver  minerals — 
smaltite,  proustite,  pyrar- 
gyrite;  native  bismuth 
and  arsenic,  calcite. 


422 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Green,  red,  brown,  yellow,  or  black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

GRAPHITE  (Plumbago,          Hexagonal                             Dull                    Dark  gray 
black  lead)   C  —  Tabular,  rare                 Opaque              Iron  black 

C  M — Scaly,  foliated,  gran- 

ular, earthy,  sooty 


192 


CHLORITE  (Pyrochlorite,     Monoclinic  Dull  Black 

clinochlorite)   C — Tabular,  six-s  i  d  e  d,   Submetallic      Greenish 
is?  often  bent,  twisted    Translucent        black 

M — Foliated,  scaly,  gran-    to  opaque 
ular,  earthy 


297 

Uraninite  (Pitchblende) 

Cubic                                     Pitch-like 

Pitch  black 

C  —  Octahedral,  rare           Submetallic 

Brownish 

UO3,  UO2,  PbO,  etc. 

M  —  Botryoidal,     colum-  Dull 

black 

nar,    curved    lamel-  Opaque 

Greenish 

lar,    granular,    com- 

black 

pact,    apparently 

262 

amorphous 

SIDERITE 

Hexagonal                            Vitreous 

Brownish 

C  —  Rhombohedral,             Dull 

black 

FeC03 

curved     or     saddle-  Translucent 

Black 

shaped,  common  to  opaque 

M — Cleavable,  granular, 
compact,  botryoidal 


248 


SPHALERITE  (Black  Jack)  Cubic  Submetallic  Black 

C — Tetrahedral,  common  Resinous  Yellowish 

ZnS  M — Cleavable,   fine  and  Opaque  to  black 

coarse  grained,  com-     translucent  Brownish 

pact  black 


205 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


423 


Hardness  1  to  6 


Cleavage  =  C 
Hard~             Streak                  Fraature  =  F         ^pe 
ness                                           Tenacity 

cific          Characteristics  and 
vity                 Associates 

1.          Dark  gray              C  —  Basal,     perfect        1  .  9      Greasy  feel.    Marks  paper. 
2.          Iron  black                     (scales)                      2.3        Of  ten  impure.    In  crystal- 
Scales  flexible                              line  limestone  with  garnet, 
spinel,  pyroxenes,  amphi- 
boles  ;  also  in  shale,  gneiss, 
mica  schist. 

1.          Pale  green              C  —  Basal,  conspicu-       2  .  6      Laminae    flexible    but    in- 
2.6                                              ous,  when                 3.          elastic,       with       slightly 
foliated                                  soapy  feel.     Common  in 
F  —  Scaly,  earthy                         schists     and     serpentine. 
Tough  to  brittle                         With  magnetite,  magne- 
site,      garnet,      diopside. 
Often  as  scaly  or  dusty 
coating  on  other  minerals. 
Pseudomorphous        after 
garnet. 

3.          Olive  green             F  —  Conchoidal,  un-        4  .  8      Pitch-like  appearance  and 
5.6        Dark  brown                  even                           9  .  7       fracture       characteristic. 
Brownish  black      Brittle                                           Fresh    material     is    hard 
Grayish  black                                                              and    heavy.     With   lead, 
silver,  bismuth,  minerals; 
also  pyrite,  orthite. 

3.6       Yellowish  brown    C — Rhombohedral, 
4.  perfect,    con- 

spicuous 

F — Conchoidal 

Brittle 


3.7  Curved  crystals,  cleavage, 
3.9  and  rather  high  specific 
gravity  characteristic.  In 
ore  deposits;  beds  and 
concretions  in  limestone 
and  shale.  With  pyrite, 
chalcopyrite,  galena,  tet- 
rahedrite,  cryolite. 


3.5        Dark  brown  C — Dodecahedral 

4.          Yellowish  brown          perfect,  usually 
Gray  conspicuous 

F — Conchoidal 

Brittle 


3.9  Color  and  streak  vary  with 
4.2  impurities.  When  mass- 
ive distinguished  from 
siderite  by  cleavage.  Ex- 
tensively in  limestone. 
With  galena,  chalcopy- 
rite, pyrite,  barite,  fluor- 
ite,  siderite,  rhodochro- 
site. 


424 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Green,  red,  brown,  yellow,  or  black 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Huebnerite                                 Monoclinic                           Resinous           Brownish 
C  —  Long  fibrous,  bladed,  Submetallic        black 
MnWO4                                         stalky;   often  Translucent      Black 

260 


divergent,      without     to  opaque 
good  terminations 
M — Compact,     lamellar, 
granular 


WOLFRAMITE 
(Fe,Mn)WO4 

261 


Monoclinic  Submetallic       Dark  gray 

C — Thick  tabular,  short  Opaque  Brownish 


columnar,  often 
large 

M: — Bladed,  curved  lam- 
ellar, granular 


black 
Iron  black 


Ferberite 
FeWO4 

261 

Monoclinic                           Submetallic 
C  —  Wedge  shaped,  short  Splendent 
prismatic,  tabular       Opaque 
M  —  Fan-shaped      aggre- 
gates, bladed,  granu- 
lar, compact 

Iron  black 
Brownish 
black 

HORNBLENDE  (Amphi- 
bole) 
Silicate  of  Ca,  Mg,  Fe,  Al, 
etc. 

312 

Monoclinic                           Vitreous 
C  —  Long  prismatic,             Silky 
prism     angle     124°;  Translucent 
often  with  rhombo-     to  opaque 
hedral-like  termina- 
tions 
M—  Bladed,       fibrous 
granular,  compact 

Pitch  black 
Greenish 
black 
Brownish 
black 

AUGITE  (Pyroxene)  Monoclinic  Vitreous  Pitch  black 

C — Short  prismatic;  Submetallic  Greenish 

Silicate  of  Ca,  Mg,  Fe,  Al,  thick  columnar,  Translucent  black 

etc.  prism  angle  87°  to  opaque  Brownish 

M — Compact,    granular,  black 
disseminated 


307 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


425 


Hardness  1  to  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

4.6        Yellowish  brown    C — Clinopinacoidal, 
6.6  perfect,    c  o  n- 

spicuous 
Brittle 


6.7  Structure,  cleavage,  and 
7 . 3  high  specific  gravity  char- 
acteristic. In  quartz 
veins.  With  wolframite, 
fluorite,  pyrite,  scheelite, 
galena,  tetrahedrite. 


5.          Dark  reddish 
5.5          brown 
Black 

C  —  Clinopinaeoidal, 
perfect,    c  o  n- 
spicuous 
F  —  Uneven 
Brittle 

7.1      Distinguished  from  hue- 
7  .  5       bnerite  by  streak.    Pow- 
der may  be  slightly  mag- 
netic.    With  cassiterite, 
quartz,    mica,    fluorite, 
apatite,  scheelite,  molyb- 
denite, huebnerite. 

6.           Dark  brown 
6.5        Brownish  black 

C  —  Clinopinacoidal, 
perfect 
F  —  Uneven 
Brittle 

7.5     In  granites  and  pegmatites. 
With    quartz,    chalcopy- 
rite,  galena,  scheelite. 

Grayish  green 
Grayish  brown 
Yellow 


C — Prismatic,  per- 
fect, often  con- 
spicuous— 124° 

Brittle 


2.9  Simple,  pseudohexagonal 
3 . 3  crystals,  and  cleavage  at 
124°  important.  Very 
common;  in  nearly  all 
types  of  rocks.  Withcal- 
cite,  quartz,  feldspar,  py- 
roxene, chlorite. 


Pale  green 
Grayish  green 


C — Prismatic,  per- 
fect, conspicu- 
ous— 87° 

Brittle 


3.2  Crystals  usually  eight- 
3.6  sided,  more  rarely  four- 
sided  ;  pseudotetragonal 
with  prism  angles  of  87° 
and  93°.  Cleavage  less 
distinct  than  on  horn- 
blende. Common  in  basic 
eruptive  rocks  and  crys- 
talline limestones. 


426 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Green,  red,  brown,  yellow,  or  black 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Psilomelane 

MnO2,  BaO,  H2O,  etc. 
253 


Amorphous  ?  Submetallic  Iron  black 

M — Botryoidal,    r  e  n  i-  Dull  Bluish  black 

form,    stalactitic;  Opaque  Dark  gray 

smooth  surfaces 


CHROMITE 

(Fe,Cr)[(Cr,Fe)02]2 

270 


Cubic  Submetallic  Iron  black 

C — Octahedral,  rare  Pitchy  Brownish 

M — Compact,    granular,  Opaque  black 
disseminated  grains 


Orthite  (Allanite) 

Cai(Al,Ce,Pe),(A1.0H) 

(Si04)3 


Monoclinic  Submetallic  Black 

C — Tabular,  rare  Greasy  Pitch  black 

M — Compact,    granular,  Translucent  Brownish 

bladed,  disseminated       to  opaque         black 

grains 


287 


Streak — Green,  red,  brown,  yellow,  or  black 


RUTILE 
TiO2  or  TiTi04 

224 


Tetragonal  Adamantine     Iron  black 

C — Prismatic,    vertically  Metallic  Brownish 

striated;      twinned,  Opaque  to          black 
yielding  knee-shaped     transparent    Reddish  black 
or  rosette  forms 
M — Compact,     dissemi- 
nated 


CASSITERITE 

SnO2  or  SnSnO4 


226 


Tetragonal 

C — Thick  prismatic;          Dull 

knee-shaped  twins       Translucent 

quite  common  to  opaque 

M — Compact,    reniform, 

botryoidal,   rounded 

pebbles,   often  with 

internal,  radial 

fibrous  structure 


Submetallic      Black 

Brownish 
black 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


427 


Hardness  1  to  6 


**             Str 

ness 

Cleavage  =  C        ^ 
eak                  Fracture  =  F 

m             'A                              vjrra 

Tenacity 

eific          Characteristics  and 
vity                 Associates 

5.         Black                      F  —  Conchoidal,  un-       3  .  7      Often  with  fine  sooty  coat- 
6.         Brownish  black            even                          4.7       ing  of  pyrolusite.     With 
Brittle                                         other     manganese     min- 
erals; also  limonite,  bar- 
ite. 

5.5        Dark  brown           C  —  Indistinct                  4.3      May  be  slightly  magnetic. 
Grayish  brown      F  —  Uneven,   con-       4.6       Pitch-like  appearance 
choidal                                  characteristic.     With  ser- 
Brittle                                           pentine,  talc,  chrome  gar- 
net;  also  in  black  sands, 
platinum  placers. 

6.5        Pale  brown             C  —  Pinacoidal,    in-        3  .        Often  covered  with  yellow- 
6.          Grayish  brown             distinct                      4  .          ish    or    brownish    altera- 
F  —  Uneven,   con-                    tion     product.     Dissemi- 
choidal                                  nated  through  the  more 
Brittle                                           acid  igneous  rocks;   also 
in  limestones.    With  mag- 
netite,    epidote,     quartz, 
feldspar. 

Hardness  over  6 


6. 
7. 

Pale  yellow 
Pale  brown 

C  —  Prismatic,    py-       4  .  2 
ramidal,    not           4  .  3 
conspicuous 
F  —  Uneven 
Brittle 

Not  as  heavy  as  cassiter- 
ite.    Often  in  fine  hair- 
like    inclusions.    Widely 
distributed.  With  quartz, 
feldspar,  hematite,  ilmen- 
ite,  chlorite. 

6.  Pale  brown  C — Indistinct  6 . 8      Distinguished  by  high  spe- 

7.  Pale  yellow  F — Uneven  7 .          cific    gravity.    In    veins 

Brittle  cutting  granite,  gneiss ;  in 

alluvial  deposits  as  stream 
tin.  With  quartz,  wol- 
framite, scheelite,  arseno- 
pyrite,  molybdenite,  tour- 
maline, fluorite,  apatite, 
chlorite,  mica. 


428 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak    Green,  red,  brown,  yellow  or  black 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CORUNDUM,  variety  Hexagonal  Dull  Dark  gray 

Emery        M — Fine  to  poarse  granu-  Submetallic      Black 
A12O3,  with  Fe3O4,  Fe2O3,  ular  Opaque 

SiO2 


228 

SPINEL,  varieties  Cubic  \itreous  Black 

Hercynite  C — Octahedral,  small         Dull  Brownish 

R"(R"'O2)2         Picotite       M — Compact,    granular,   Nearly  black 

IT'  =  Mg,  Fe,  disseminated  grains      opaque 

Zn,  Mn 
R'"  =  Al,  Fe 
267 


Streak — Uncolored,  white,  or  light  gray 


APATITE,  variety  Hexagonal  Dull 

Phosphate  rock  M — Compact,       fibrous,   Opaque 
Ca6F(PO4)3,  in  part  nodular,      reniform, 

earthy 


Black 


273 


BIOTITE   Black  mica) 

(K,H)2(Mg,Fe)2(Al,Fe)2. 
(Si04)3 


294 


Monoclinic  Pearly  Black 

C — Tabular,    with    hex-  Submetallic  Brownish 
agonal  or  rhombohe-  Transparent       black 

dral  habit  to  opaque  Greenish 

M — Plates,  disseminated  black 

scales 


CALCITE,  varieties 
CaC03 


Hexagonal  Vitreous  Dark  gray 

Limestone  M — Cleavable,  granular,  Dull  Brownish 

Marble  fibrous,  banded,  Translucent  black 

Stalactites,  etc.  stalactitic,  oolitic,  to  opaque  Black 

Calcareous  tufa         porous,  compact, 
Travertine  crusts,  shells 


242 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


429 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   -  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

7.          Yellowish                C  —  Indistinct                  3.7      Corundum  mixed  with  iron 

9.           brown                    F  —  Uneven                      4.3        ore.  Powder  may  be  mag- 

Black                       Brittle  to  tough                          netic.     With    mica,    am- 

phibole,  chlorite,  spinel; 
in  crystalline  limestones, 
schists,  peridotites. 


7.5        Grayish  green         C  —  Octahedral,   in- 
8.          Pale  brown                    distinct 
F  —  Conchoidal 
Brittle 

3  .  9      Commonly  in  basic  igneous 
4  .  1        rocks,  especially  the  oliv- 
ine-b  earing  types.      With 
olivine,    serpentine,    cor- 
undum, magnetite,  horn- 
blende, garnet. 

Hardness  1  to  3 


White 


F — Conchoidal,  un-  3 . 1  More  or  less  impure 
even  3.2  masses,  frequently 

Brittle  resembling  compact  bi- 

tuminous limestone.  In- 
dependent beds,  nodules, 
or  concretions. 


2.5        White  C — Basal,    perfect, 

3.          Grayish  conspicuous 

Tough,   lamellae  of 
fresh  biotite 
very  elastic 


2 . 7      Easily  recognized  by  struc- 

3.2        ture,     highly    perfect 

cleavage,    and   elasticity. 

Important  constituent  of 

many  igneous  and  meta- 

morphic     rocks  — granite, 

syenite,  gneiss. 


3. 


White 
Gray 


C — Rhombohedral , 

perfect 

F — Conchoidal 
Brittle 


2 . 7  Rhombohedral  cleavage 
generally  obser  ved. 
Cleavages  often  striated. 
Yields  bituminous  odor 
when  struck  with  ham- 
mer. To  distinguish  var- 
ieties, see  reference. 


430 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

ANHYDRITE 
CaSO4 

254 


Orthorhombic  Vitreous  Dark  gray 

C — Thick   tabular,   pris-  Pearly  Blackish 

matic,  rare  Translucent 
M — Granular,    compact,     to  opaque 

fibrous,        lamellar, 

cleavable 


SERPENTINE 


Orthorhombic  ?  Greasy  Greenish 

C — Unknown  Waxy  black 

M — Compact,  columnar,  Translucent  Brownish 

fibrous,        lamellar,  to  opaque         black 

granular 


297 


APATITE,  variety  Hexagonal 

Phosphate  rock  M  —  Compact, 
Ca6F(PO4)3,  in  part  nodular, 

earthy 


Dull 

fibrous,   Opaque 
reniform, 


Black 


273 


SPHALERITE  (Black  Jack)  Cubic  Submetallic  Black 

C — Tetrahedral,  common  Opaque  to  Brownish 
ZnS                                          M — Cleavable,     fine     or     translucent       black 

coarse  grained,  com-  Yellowish 
pact  black 

205 


Huebnerite 
MnW04 

260 


Monoclinic  Resinous 

C  —  Long  fibrous,  bladed,    Submetallic 

stalky    often  diver-    Translucent 

gent,    without  good      to  opaque 

terminations 
M  —  Compact,     lamellar, 

granular 


Brownish 

black 
Black 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


431 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.          White                      C  —  Pinacoidal,  per-        2  .  8      Color     due     to     organic 
3.5                                              feet,     3     direc-        3.          matter.        Pseudocubical 

tions  at  90° 
F — Conchoidal 
Brittle 


cleavage  som  etimes 
noted.  Granular  varie- 
ties resemble  marble.  In 
limestones,  shales.  With 
halite,  gypsum. 


White 


F — Conchoidal,  2.5  Smooth  and  greasy  feel, 

splintery  2.8  Often  spotted,  clouded, 

Brittle  multi-colored.  Some- 

times crossed  by  seams 
of  asbestos  (chrysotile). 
With  magnesite,  calcite, 
chromite,  garnierite,  py- 
rope,  platinum. 


White 


F — Conchoidal,  un-        3 . 1 
even  3 . 2 

Brittle 


More  or  less  impure  masses 
frequently  resembling 
compact,  bituminous 
limestone.  Independent 
beds,  nodules,  or  con- 
cretions. 


3.5 
4. 


Grayish 


C — Dodecahedral 
perfect,  usually 
conspicuous 

F — Conchoidal 

Brittle 


3 . 9  Color  and  streak  vary  with 
4 . 2  impurities.  Extensively 
in  limestones  with  galena, 
chalcopyrite,  pyrite,  bar- 
ite,  fluorite,  siderite,  rho- 
dochrosite. 


4.5 
5.5 


Greenish  gray 


C — Clinopinacoidal, 
perfect,  c  o  n- 
spicuous 

Brittle 


6.7  Structure,  cleavage,  and 
7 . 3  specific  gravity  character- 
istic. In  quartz  veins. 
With  wolframite,  fluorite, 
pyrite,  scheelite,  galena, 
tetrahedrite. 


432 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

TITANITE  (Sphene) 
GaTiSi06 


Monoclinic  Vitreous  Black 

C — Wedge-    or  envelope-  Submetallic       Brownish 
shaped  when  dissem-   Translucent         black 
inated;    tabular    or     to  opaque 
prismatic   when    at- 
tached 
M — Compact,  lamellar 


HORNBLENDE  (Amphi-       Monoclinic                           Vitreous  Pitch  black 

bole)  C — Long  prismatic,  prism  Silky  Greenish 

Silicate  of  Ca,  Mg,  Fe,  Al,           angle      124°,     often  Translucent  black 

etc.           with  rhombohedral-     to  opaque  Brownish 

like  terminations  black 
M— Bladed,  fibrous, 
312                                                granular,  compact 


AUGITE  (Pyroxene)  Monoclinic  Vitreous  Pitch 

C — Short  prismatic,  Submetallic  black 

Silicate  of  Ca,  Mg,  Fe,  Al,  thick  columnar,  Translucent  Greenish 

etc.  prism  angle  87°  to  opaque  black 

M — Compact,  granular,  Brownish 
307                                                disseminated  black 


Orthite  (Allanite) 

Ca2(Al,Ce,Fe)2(Al.OH) 

(Si04)3 

287 


Monoclinic  Submetallic  Black 

C — Tabular,  rare '  Greasy  Pitch  black 

M — Compact,    granular,  Translucent  Brownish 

bladed,  disseminated     to  opaque  black 

grains 


Streak — Uncolored,  white,  or  light  gray 


LABRADORITE  (Feldspar)    Triclinic  Vitreous 

C — Thin    tabular,    often  Pearty 


Silicate  of  Na,Ca,Al 


321 


with    rhombic  cross-  Translucent 
section  to  nearly 

M — Compact,  cleavable,      opaque 
granular 


Dark  gray 
Greenish 
gray 


1.     DARK  GRAY  OR  BLACK  IN  COLOR 


433 


Hardness  3  to  6 

Hard- 
ness 

Streak 

Cleavage  = 
Fracture   — 
Tenacity 

C 

F 

Specific 
Gravity 

Characteristics  and 
Associates 

5. 
5.5 

White                       C  —  Prismatic, 
Gray                              spicuous 

con-         3.4      With  feldspars,  pyroxenes, 
part-        3  .  6        amphiboles,  chlorite, 

ings  often  noted 
F — Conchoidal 
Brittle 


scapolite,  zircon. 


5.          Gray 
6.          Greenish  gray 
Brownish  gray 

C  —  Prismatic,  per- 
fect, often  con- 
spicuous —  124° 
Brittle 

2.9 
3.3 

Simple,     pseudohexagonal 
crystals,     and     cleavage 
(124°)    important.     Very 
common.     In    nearly   all 
types    of    rocks.        With 
feldspars,  quartz,  pyrox- 
enes, chlorite,  calcite. 

5.          White 
6.          Gray 
Greenish  gray 

C  —  Prismatic,   per- 
fect,   conspicu- 
ous —  87°,     less 
distinct  than  on 
hornblende. 
Brittle 

3.2 
3.6 

Crystals     usually     eight- 
sided,   more  rarely  four- 
sided  ;     pseudotetragonal 
with  prism  angles  of  87° 
and    93°.     In  basic  rocks 
and  limestones. 

6.5       Gray 
6.          Greenish  gray 

C  —  Pinacoidal,    in- 
distinct 

3. 
4. 

Often  covered  with  yellow- 
ish   or    brownish    crust. 

Brownish  gray      F — Uneven,    c  o  n- 

choidal 
Brittle 


Disseminated  in  the  more 
acid  igneous  rocks;  lime- 
stones. With  magnetite, 
epidote,  quartz,  feldspars. 


Hardness  over  6 


6.          White 
6.5 

C  —  Basal,    brachy- 
pinacoidal,  per- 
fect,   conspicu- 
ous— 86° 
F  —  Uneven,    c  o  n- 
choidal 
Brittle 

2  .  7      Often  with  play  of  colors  — 
yellow,  green,   blue,   red. 
Inclined     cleavages     are 
striated.     In   basic   igne- 
ous rocks.     With  pyrox- 
enes, amphiboles. 

434 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

EPIDOTE  Monoclinic  Vitreous 

C — Prismatic,    elongated  Translucent 

Ca»(Al,Fe)i(Al.OH)(^O4)i         and  deeply  striated     to  opaque 

parallel  to  I  axis; 
generally  terminated 
on  one  end  only 
M — Columnar,  fibrous, 
parallel  and  diver- 
gent, granular 


Greenish 
black 


286 

RUTILE 

Tetragonal 

Metallic 

Iron  black 

C  —  Prismatic,    vertically 

Adamantine 

Brownish 

Ti02  or  TiTi04 

striated;       twinned, 

Opaque  to 

black 

yielding  knee-shaped 

translucent 

Reddish 

or  rosette  forms 

black 

M  —  Compact,      dissemi- 

nated 

224 

CASSITERITE 

Tetragonal 

Submetallic 

Black 

C  —  Thick    prismatic, 

Dull 

Brownish 

SnO2  or  SnSnO4 

knee-shaped     twins, 

Translucent 

black 

quite  common 
M — Compact,    reniform, 
botryoidal,   rounded 
pebbles,    often  with 
internal,  radial 
fibrous  structure 


to  opaque 


226 


GARNET,  varieties  Cubic 

Andradite    C — Dodecahedrons, 

R3"R2'"(SiO4)3  Almandite          tragonal    trisoctahe-     to  opaque 
R"  =  Ca,  Fe,  Mg  drons,    alone    or   in 

R'"  =  Al,  Fe  combination 

M — Granular,    compact, 
lamellar,       dissemi- 
nated, sand 
290 


Vitreous  Velvety  black 

te-  Translucent      Brownish 
black 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


435 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 

Associates 

6.          White                      C  —  Basal,  perfect           3  .  3      Crystals    are    often    dark 
7.          Grayish                   F  —  Uneven                      3.5        green  or  blackish  green, 
Brittle                                           massive  aggregates  lighter 

colored.  Widely  dis- 
tributed. With  quartz, 
feldspar,  garnet,  horn- 
blende, pyroxene,  mag- 
netite, native  copper. 


Gray 


C — Prismatic,    py-        4 . 2      Not  as  heavy  as  cassiterite. 


Yellowish  white  ramidal,     not 

Brownish  white  conspicuous 

F — Uneven 

Brittle 


4.3  Often  in  hair-like  in- 
clusions. Widely  dis- 
tributed. With  quartz, 
feldspar,  hematite,  ilmen- 
ite,  chlorite. 


6.  White  C — Indistinct  6 . 8      Distinguished  by  high  spe- 

7.  Yellowish  white     F — Uneven  7 .          cific    gravity.     In    veins 
Brownish  white     Brittle  cutting  granite,  gneiss;  in 

alluvial  deposits  as  stream 
tin.  With  quartz,  wolf- 
ramite, scheelite,  molyb- 
denite, tourmaline,  fluor- 
ite,  mica,  chlorite. 


6.5 
7.6 


White 


C — Dodecahedral , 
usually  indis- 
tinct 

F — Conchoidal,  un- 
even 

Brittle 


3.8  Andradite,  commonly  with 
4.2  magnetite,  epidote,  feld- 
spars, nephelite,  leucite ; 
almandite,  with  mica, 
staurolite,  andalusite,  cy- 
anite,  tourmaline. 


436 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

QUARTZ,  Phanerocrystal-      Hexagonal  Vitreous  Grayish  black 

line  variety  C — Prismatic,      horizon-  Transparent  Brownish 

SiO2  Smoky  quartz  tally  striated  to  trans-  black 

M — Compact,  granular        lucent 


Cryptocrystalline  Hexagonal  Waxy  Grayish  black 

varieties  Fine   crystalline   masses,  Vitreous  Brownish 

Chalcedony  banded,  nodular,  Translucent  black 

Onyx  botryoidal,  to  opaque  Velvet  black 

Flint  stalactitic 

220 


TOURMALINE 

M9'Al3(B.OH)2Si4O19 
M'  =  Na,  K,  Li,  Mg,  Fe 


284 


Hexagonal  Pitchy 

C — Prismatic,    vertically  Vitreous 
striated;  terminated  Translucent 
with  broken  or  rhom-    to  opaque 
bohedral-like       sur- 
faces; well  developed 
crystals    are    hemi- 
morphic 

M — Compact,   divergent 
columnar 


Pitch  black 
Brownish 

black 
Bluish  black 


STAUROLITE 


Fe(A10)4(A1.0H)(Si04)s 


Orthorhombic  Vitreous  Brownish 

C — Prismatic;  twins  plus-  Dull  black 

(+)     or    X-shaped,   Translucent      Dark  gray 

well  developed,  often     to  opaque 

large 


279 


SPINEL,  varieties  Cubic  Vitreous  Brownish 

Pleonaste  C — Octahedral,  well  de-  Dull  black 

R//(R"/O2)2          Gahnite  veloped,  common  Nearly  Grayish  black 

R"  =  Mg,  Fe,     Dysluite  M — Compact,    granular,     opaque1  Greenish 

Zn,  Mn  disseminated  grains  black 
R'"  =  Al,  Fe 


267 


1.  DARK  GRAY  OR  BLACK  IN  COLOR 


437 


7.          White 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Indistinct  2.6      Characteristic     conchoidal 

F — Conchoidal,  fracture  and  glassy  luster, 

conspicuous  Common       in       granitic 

Brittle  rocks. 


7.          White 


C — Indistinct  2.6      Couchoidal  fracture  char- 

F — Conchoidal,  acteristic.         Chalcedony, 

conspicuous  waxy        luster;        onyx, 

Brittle  to  tough  banded;    flint,    generally 

with  white  coating;  basan- 
ite,  velvet  black. 


7.          White 
7.6       Gray 


C — None 

F — Conchoidal,  un- 
even 
Brittle 


2.9  Spherical  triangular  cross- 
3.2  section,  coal  bls,ck  color, 
and  lack  of  cleavage  im- 
portant. In  pegmatites; 
metamorphic  rocks;  al- 
luvial deposits.  With 
quartz,  feldspar,  cassiter- 
ite,  beryl,  topaz,  fluorite. 


7. 
7.5 


White 
Gray 


C — Brachypina- 
coidal 

F — Conchoidal,  un- 
even 

Brittle 


3.4  Fresh  crystals  usually 
3 . 8  possess  bright  and  smooth 
faces,  when  altered  dull, 
rough,  softer,  and  with 
colored  streak.  In  meta- 
morphic rocks — gneiss, 
mica  schist,  slate.  With 
cyanite,  garnet,  tourma- 
line, sillimanite. 


7.6 
8. 


White 
Grayish 


C — Octahedral,  in-        3.6 
distinct  4 . 4 

F — Conchoidal 


Commonly  as  contact  min- 
eral in  granular  lime- 
stones; in  more  basic 
igneous  rocks;  rounded 
grains  in  placers.  With 
calcite,  chondrodite,  ser- 
pentine,corundum,  graph- 
ite, pyroxene,  phlogopite. 


438 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

DIAMOND,  varieties               Cubic                                    Adamantine     Black 
Diamond  proper  C  —  Octahedrons,    hexoc-  Vitreous             Dark  gray 
C                Bort                               tahedrons,      usually  Translucent 
Carbonado                    with  curved  surfaces     to  opaque 

M — Rounded  or  irregular 
grains  or  pebbles,  of- 
ten with  radial  struc- 
ture 


188 


B.     MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Red,  brown,  or  yellow 


BAUXITE 
A12O(OH)4 


Never  in  crystals  Dull  Red 

M — Pisolitic,  oolitic,  Earthy  Reddish 

rounded        dissemi-  Opaque  brown 

nated    grains,    clay- 
like,  earthy 


235 


HEMATITE,  varieties  Hexagonal                            Dull                   Brownish 

Red  ocher  M — Fine   granular,  Opaque               red 

Fe2O3               Oolitic  earthy,    oolitic,    re-                             Cherry  red 

Fossiliferous  placement  of  shells 
230 


REALGAR 
AsS 
203 


Monoclinic  Resinous  Aurora  red 

C — Short  prismatic,  rare  Transparent  Orange 
M — Granular,    compact,     to  trans-  yellow 

incrustations  lucent 


CINNABAR 
HgS 

215 


Hexagonal  Adamantine 

C — Rhombohedral,  thick  Dull 

tabular,  small  Transparent 

M — Fine  granular,  to  opaque 

fibrous,     earthy 

coatings 


Scarlet  red 
Brownish   red 


1.    DARK,  GRAY  OR  BLACK  IN  COLOR 


439 


10.          Ash  gray 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Octahedral,  per- 
fect (diamond 
proper) 

F — Conchoidal 

Brittle 


3 . 1  Diamond  proper,  crystals 
3.5  and  cleavage  fragments; 
bort,  translucent  with 
radial  structure,  also 
crystal  fragments;  carbon- 
ado, granular  to  com- 
pact, opaque.  In  ser- 
pentine rocks — kimberl- 
ite — called  blue  ground,  in 
placers.  With  pyrope, 
magnetite,  chromite, 
zircon. 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


Hardness  1  to  3 


1.          Reddish                   F—  Earthy                       2.5 
3.         Yellowish               Brittle                             2.6 

Color  and  streak  variable. 
Clay  odor  when  breathed 
upon.  Distinguished  from 
clay  by  structure.  With 
clay  or  kaolinite  in  nod- 
ules, grains,  or  irregular 
deposits  in  limestone  or 
dolomite. 

1.          Cherry  red              C  —  None                         4  .  9 
3.          Reddish  brown      F  —  Earthy                      5.3 
Brittle 

Red  ocher,  red  earthy 
variety;  oolitic  hematite, 
fish-egg  structure;  fossil- 
iferous  hematite,  replace- 
ment of  shells. 

1.5        Orange  yellow        C  —  Clinopinacoidal,       3.4 
2.                                                basal                          3.6 
F  —  Co  nchoidal 
Slightly  sectile 

Frequently  disseminated  in 
clay  or  dolomite.  With 
orpiment,  stibnite,  native 
arsenic,  pyrite,  barite,  cal- 
cite. 

2.          Scarlet                     C  —  Prismatic,     not        8. 
2.5        Red  brown                    conspicuous              8.2 
F  —  Uneven 
Brittle  to  sectile 

Characterized  by  color, 
streak,  and  high  specific 
gravity.  Disseminated 
through  silicious  rocks. 
With  native  mercury,  py- 
rite, marcasite,  realgar, 
stibnite. 

440 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Proustite 

Ag3AsS3 

217 


Hexagonal  Adamantine     Scarlet 

C — Small,  complex,  rare    Dull  Vermilion 

M — Compact,      dissemi-  Translucent 
nated,  crusts,  bands      to  trans- 
parent 


Crocoite 
PbCr04 


Monoclinic  Adamantine      Hyacinth  red 

C — Prismatic,  acicular  Greasy  Aurora  red 

M — Columnar,  granular,  Translucent 
crusts 


258 


Pyrargyrite 
AgsSbS3 

217 


Hexagonal  Adamantine 

C — Small,  complex,  rare    Metallic 
M — Compact,      dissemi-  Transparent 
nated,  crusts,  bands     to  opaque 


Dark  red 


Wulfenite 
PbMoO4 
259 


Tetragonal  Resinous 

C — Square,  thin  tabular,  Adamantine 
more  rarely  pyrami-  Transparent 
dal  to  trans- 

M — Coarse,  fine  granular     lucent 


Orange  red 
Bright  red 


Vanadinite 
Pb6Cl(V04), 
275 


Hexagonal  Resinous  Ruby  red 

C — Prismatic,   small,    at  Translucent      Brownish  red 

times  skeletal  to  opaque       Orange  red 

M — Compact,    globular, 
fibrous,  crusts 


Streak — Red,  brown,  or  yellow 


HEMATITE,  varieties  Hexagonal  Submetallic 

Argillaceous  M — Compact,    granular,   Dull 
FejOa  Compact  columnar,  splintery,   Opaque 

radiated  reniform  or 
230  botryoidal 


Brownish  red 
Dark  red 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


441 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

2.5        Scarlet                     C  —  Imperfect                  5.5      Light  ruby  silver  ore.     Dis- 
Aurora  red              F  —  Conchoidal                5  .  6        tinguished  from  cinnabar 
Brittle                                           by  associates.     With  py- 

rargyrite,  in  veins  with 
other  silver  minerals  and 
galena.  Compare  pyrar- 
gyrite. 


2.5        Orange  yellow 

C  —  Basal,  prismatic 
F  —  Conchoidal,  un- 
even 
Sectile 

5.9      Resembles    potassium    bi- 
6.1        chromate  in  color.  Altera- 
tion   product    of   galena. 
With  galena,  quartz,  py- 
rite,   vanadinite,   wulfen- 
ite. 

2.5        Cherry  red 
3.          Purplish  red 

C  —  Indistinct 
F  —  Conchoidal 
Brittle 

5  .  8      Frequently  as  gray  or  dark 
red  bands.     Darker  than 
proustite  —  dark  ruby  sil- 
ver ore.     With  proustite, 
in  veins  with  other  silver 
minerals  and  galena. 

3.          Lemon  yellow 
Pale  yellow 

C  —  Pyramidal,    in- 
distinct 
F  —  Conchoidal,  un- 
even 
Brittle 

6.3      Square   plates,    sometimes 
7.          with  forms  of  the  third 
order.     With    lead    min- 
erals —  galena,     pyromor- 
phite,  vanadinite. 

3.          Pale  yellow 
Yellow 

C  —  None 
F  —  Conchoidal,  un- 
even 
Brittle 

6.7      Crystal  faces  smooth  with 
7.2        sharp  edges.     With  lead 
minerals    but     never    in 
large  quantities. 

Hardness  over  3 


3. 


Cherry  red 
Reddish  brown 


C — None 

F — Uneven,  splint- 
ery 
Brittle 


Argillaceous  hematite,  im- 
pure from  clay,  sand, 
jasper;  compact  hematite, 
usually  quite  pure. 


442 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Red,  brown,  or  yellow 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

SPHALERITE 
ZnS 

205 


Cubic  Greasy  Brownish  red 

C — Tetrahedral,  common  Submetallic  Yellowish  red 

M — Cleavable,  fine  to  Translucent 

coarse  granular,  to  opaque 

compact 


CUPRITE 

Cu20 

232 


Cubic  Adamantine     Cochineal  red 

C — Octahedrons,  dodeca-  Dull  Brick  red 

hedrons,  alone  or  in  Translucent      Dark  red 
combination  to  opaque 

M — Compact,  granular, 
earthy ;  slender  crys- 
tal aggregates  (chal- 
cotrichite) 


Zincite 
ZnO 


Hexagonal  Adamantine      Dark  red 

C — Hemimorphic,  rare  Vitreous  Blood  red 

M — Compact,    granular,  Translucent 
foliated  to  opaque 


228 


Huebnerite 
MnWO4 

260 


Monoclinic  Greasy  Brownish  red 

C — Long,  fibrous,  bladed,  Submetallic 

stalky;  often  diver-  Translucent 

gent,    without  good     to  opaque 

terminations 
M — Compact,    lamellar, 

granular 


WOLFRAMITE 

(Fe,Mn)WO4 

261 


Monoclinic  Submetallic 

C — Thick  tabular,  short  Opaque 

columnar,  often  large 
M — Bladed,  curved  lam- 
ellar, granular,  com- 
pact 


Brownish  red 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


443 


3.5 
4. 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

/~i 

=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

Pale  yellow 
Brownish  yellow 


C — Dodecahedral, 
perfect,  usually 
conspicuous 

F — Conchoidal 

Brittle 


3 . 9  Color  and  streak  vary  with 
4 . 2  impurities.  Extensively 
in  limestone.  With 
galena,  chalcopyrite,  py- 
rite,  barite,  fluorite,  sid- 
crite,  rhodochrosite. 


3.6        Brownish  red          C — Indistinct  5.7     Characterized      by 

4.          Dirty  brown          F — Uneven  6 . 1        ciates,  usually  with  cop- 

Brittle  per    minerals — malachite 

(green),  azurite  (blue), 
chalcocite  and  melaconite 
(black),  chalcopyrite  (yel- 
low), native  copper. 


4. 
4.5 


Orange  yellow 
Reddish  yellow 


C — Basal,  s  o  m  e- 
times  conspicu- 
ous 

F — Uneven 

Brittle 


5 . 4  Associates  important — cal- 
cite,  franklinite  (black), 
willemite  (yellow  t  o 
green),  rhodonite  (flesh 
red).  On  exposure  be- 
comes coated  with  the 
white  carbonate. 


4.6        Yellowish  brown    C — Clinopinacoidal, 
6.6  perfect,     c  o  n- 

spicuous 
Brittle 


6.7  Structure,  cleavage,  and 
7.3  specific  gravity  character- 
istic. In  quartz  veins. 
With  wolframite,  fluorite, 
scheelite,  galena,  tetra- 
hedrite. 


6. 
5.5 


Dark  reddish 
brown 


C — Clinopinacoidal, 
perfect,  conspic- 
uous 

F — Uneven 

Brittle 


7.1  Distinguished  from  hueb- 
7 . 5  norite  by  streak.  Powder 
may  be  slightly  magnetic. 
With  cassiterite,  quartz, 
mica,  scheelite,  molyb- 
denite, huebnerite. 


444 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Red,  brown,  or  yellow 


/ 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

RUTILE 

TiO2  or  TiTiO4 

224 


Tetragonal  Adamantine 

C — Prismatic,  vertically    Submetallic 
striated;       twinned,  Translucent 
yielding  knee-shaped     to  opaque 
or  rosette  forms 
M — Compact,      dissemi- 
nated 


Dark  red 
Brownish  red 


CASSITERITE 
SnO2  or  SnSnO4 


226 


Tetragonal  Adamantine 

C — Thick  prismatic;  Dull 

knee-shaped      twins  Translucent 
quite  common  to  opaque 

M — Compact,  reniform, 
botryoidal,  rounded 
pebbles,  often  with 
radial  fibrous  struc- 
ture (wood  tin) 


Brownish  red 
Yellowish  red 


Streak — Uncolored,  white,  or  light  gray 


GYPSUM 
CaSO4.2H2O 


Monoclinic  Vitreous 

C— Rare  Silky 

M — Coarse,    fine  granu-  Dull 

lar,    fibrous,  cleav-  Transparent 
able,  sand  to  opaque 


Flesh  red 
Brick  red 


264 


HALITE  (Rock  salt) 
NaCl 

236 


Cubic  Vitreous  Red 

C — Cubes,  often  skeletal  Transparent     Reddish 

or      hopper-shaped,     to  trans-          Purplish 

rare  lucent 

M — Compact,  cleavable, 

granular,        fibrous, 
crusts,  stalactitic 


Lepidolite  (Lithium  mica)        Monoclinic 

C — Short  prismatic 
(Li,H)2(F,OH)2Al2Si3O 


Pearly  Pink 

Translucent      Rose  red 

M — Granular,  coarse  or  Red  violet 

fine;  scales,  cleavable 
plates 


297 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


445 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.         Yellowish               C  —  Prismatic,  pyra-      4.2      Not  as  heavy  as  cassiterite. 

6.5        Brownish                       midal,  not  con-       4.3        Often    in    fine,    hair-like 

spicuous                                 inclusions.     Widely     dis- 

F  —  Uneven                                   tributed.     With     quartz, 

Brittle                                         feldspars,  hematite,  ilmen- 

ite,  chlorite. 

6.  Pale  yellow  C — Indistinct  6 . 8      Recognized  by  high  specific 

7.  Pale  brown  F — Uneven  7.          gravity.     In    veins    cut- 

Brittle  ting    granite,    gneiss;    in 

alluvial  deposits  as  stream 
tin.  With  quartz,  wol- 
framite, scheelite,  arseno- 
pyrite,  tourmaline,  fluor- 
ite,  apatite,  chlorite,  mica. 


Hardness  1  to  3 


1.5       White                     C  —  Clinopinacoidal, 
2.                                              perfect  conspic- 
uous;    pyrami- 
dal, orthopina- 
coidal  (crystals) 
F  —  Co  nchoidal 
Brittle,  laminae  flex- 
ible 

2.2      Ferruginous    gypsum.     In 
2.4       limestones,  shales.     With 
halite,   celestite,  sulphur, 
aragonite,  anhydrite,  ore 
deposits. 

2.          White                      C  —  Cubic,   perfect, 
2.6                                              conspicuous 
F—  Conchoidal 
Brittle 

2  .  1      Characteristic   cubical 
2.3        cleavage  and  saline  taste. 
Color  due  to  impurities. 
May  absorb  moisture  and 
become     damp.         With 
shale,  gypsum,  anhydrite. 

White 


C— Basal,  perfect 

F — Scaly,  granular        2 . 9 

Tough 


When  massive  may  re- 
semble granular  lime- 
stone. In  pegmatites, 
granites,  gneisses.  With 
red  tourmaline  (rubellite), 
amblygonite,  spodumene, 
topaz. 


446 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

PHLOGOPITE  (Bronze          Monoclinic 

mica)    C — Tabular, 
(K,H)3Mg3Al(Si04)3 


294 


Pearly 

prismatic,  Submetallic 
hexagonal  or  ortho-  Transparent 
rhombic     outline,     to  trans- 
often      large      and     lucent 
coarse 

M — Plates,  disseminated 
scales 


Copper  red 
Bronze  red 
Brownish  red 


CALCITE 
CaCOa 

242 


Hexagonal  Vitreous  Pink 

C — Scalenohedral,  rhom-  Dull  Red 

bohedral,  prismatic,  Transparent     Violet 

tabular,  often  highly     to  nearly         Amethystine 

modified,  twinned          opaque 
M — Cleavable,  granular, 

fibrous,  compact 


Wulfenite 
PbMoO4 

269 


Tetragonal  Greasy 

C — Square,  thin  tabular,  Adamantine 

more  rarely  py-  Transparent 
ramidal  to  trans- 

M — Coarse  to  fine  granu-     lucent 
lar 


Orange  red 
Bright  red 


Vanadinite 
Pb6Cl(V04)5 
275 


Hexagonal  Greasy  Ruby  red 

C — Prismatic,    small,    at  Translucent      Orange  red 

times  skeletal  to  opaque       Brownish  red 

M — Compact,    globular, 

fibrous,  crusts 


Streak — Uncolored,  white  or  light  gray 


STILBITE  (Zeolite)  Monoclinic  Vitreous  Pale  red 

C — Twinned  in  sheaf-like,  Pearly  Brick  red 

(Ca,Na2)Al2Si6Oi6.6H2O  radial,     or    globular  Transparent 

aggregates  to  trans- 

326  lucent 


Lepidolite  (Lithium  mica) 
(Li,H)2(F,OH)2Al2Si309 


297 


Monoclinic  Pearly  Pink 

C — Short  prismatic  Translucent      Rose  red 

M — Granular,  coarse  or  Red  violet 

fine ;  scales,  cleavable 

plates 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


447 


2.5 
3. 


White 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Basal,    perfect, 
conspicuous 

Tough,  laminae 
very  elastic 


2  8  When  cleavage  laminae  are 
3.  held  close  to  the  eye  in 
viewing  a  source  of  light, 
a  star-like  form  is  some- 
times observed.  Charac- 
teristic of  crystalline  lime- 
stones, dolomites,  schists. 
With  pyroxenes,  amphi- 
boles,  serpentine. 


White 


C — Rhombohedral , 
perfect,     very 
conspicuous 

F — Conchoidal 

Brittle 


2 . 7  Rhombohedral  cleavage 
characteristic,  especially 
on  crystals.  Cleavages 
often  show  striations. 
Very  strong  double  re- 
fraction observed  when 
transparent. 


White  C — Pyramidal,  in- 

Yellowish  white  distinct 

F — Conchoidal,  un- 
even 

Brittle 


6.3      Square   plates,    sometimes 
7.          with  forms  of  the  third 
order.     With    lead    min- 
erals— galena,     pyromor- 
phite,  vanadinite. 


White  C— None 

Yellowish  white     F — Conchoidal,  un- 
even 
Brittle 


6.7      Crystal  faces  smooth  with 
7.2        sharp  edges.     With  lead 

minerals    but    never    in 

large  quantities. 


Hardness  3  to  6 


3.  White  C — Pinacoidal  2  1      Radial  and  sheaf-like  struc- 

4.  F — Uneven  2 . 2       ture  important.     In  basic 
Brittle  igneous  rocks,  ore  depos- 
its.   With  chabazite,  apo- 
phyllite,  datolite  ealcite, 


White 


C— Basal,  perfect 

F — Scaly,  granular         2 . 9 

Tough 


When  massive  often  like 
granular  limestone.  In 
pegmatites,  granites, 
gneisses.  With  red  tour- 
maline (rubellite),  ambly- 
gonite,  spodumene,  topaa. 


448 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

ALUNITE  (Alum  stone) 
K2(A1.20H)6(S04)4 

262 


Hexagonal  Vitreous  Pink 

C — Rhombohedrons,    re-  Pearly  Reddish 

sembling  cubes,  Transparent       white 

tabular,  rare  to  trans- 

M — Compact,    granular,  lucent 

fibrous,  earthy 


SPHALERITE 

ZnS 

205 


Cubic  Greasy  Brownish  red 

C — Tetrahedral,  common  Submetallic  Yellowish  red 
M — Cleavable,  fine  or  Translucent 

coarse  granular,  to  opaque 

compact 


RHODOCHROSITE 

MnCO3 
248 


Hexagonal  Vitreous  Rose  red 

C — Rhombohedral,  rare     Translucent      Brownish  red 

M — Cleavable,  granular,  Pink 

compact,  botryoidal, 

crusts 


FLUORITE  (Fluor  spar) 
CaF2 

239 


Cubic  Vitreous  Red  violet 

C — Cubes,  alone  or  modi-  Transparent     Pink 

fied,  well  developed,     to  nearly         Rose  red 

common;      penetra-     opaque 

tion  twins 
M — Cleavable,  granular, 

fibrous 


CHABAZITE  (Zeolite)  ' 
CaAl2Si6Oi6.8H2O,  etc. 

327 


Hexagonal  Vitreous  Flesh  red 

C — Rhombohedral,  cube-  Translucent      Red 

like,  lenticular  to  trans- 

M — Compact  parent 


APOPHYLLITE  (Zeolite) 
H14K2Ca8(SiO3)i6.9H2O 


326 


Tetragonal  Vitreous  Pale  red 

C — Prismatic,  pyramidal,  Pearly  Flesh  red 

pseudocubical,  tabu-  Transparent     Rose  red 

lar  to  nearly 

M — Lamellar,    granular,  opaque 

compact 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


449 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  = 
Fracture  = 
Tenacity 

C 
F 

Specific 
Gravity 

Characteristics  and 
Associates 

3.5        White                      C—  Basal 

2  .  6      Hardness  often  greater  dm 

4.                                         F  —  Splintery, 

con-        2.8        to   admixture  of  quartz 

choidal,  earthy 
Brittle 


feldspar ,  then  tough.  De- 
posits and  veins  in  feld- 
spathic  rocks.  With  kao- 
lin, pyrite,  opal. 


3.5        Gray  C — Dodecahedral, 

4.          Yellowish  white  perfect,  usually 

conspicuous 

F — Conchoidal 

Brittle 


3 .9  Color  and  streak  vary  with 
4.2  impurities.  Extensively 
in  limestones.  With 
galena,  chalcopyrite,  py- 
rite, barite,  fluorite,  rho- 
dochrosite. 


3.5 
4.5 


White 


C— Rhombohedral, 
perfect,  c  o  n- 
spicuous 

F — Uneven 

Brittle 


3.3      May  turn  brown  to  black 

3.6        on  exposure,  due  to  MnO«. 

With   galena,    sphalerite, 

pyrite,    rhodonite,   psilo- 

melane,  silver  minerals. 


White 


C — Octahedral,  per- 
fect, conspicu- 
ous 

Brittle" 


3.         Easily  recognized  by  crys- 
3.2        tal   form,    cleavage,    and 
hardness.          Common 
gangue  mineral  of  metallic 
ores.    With  galena,  sphal- 
erite,  cassiterite,   calcite, 
{quartz,  barite. 


White 


C — Rhombohedral, 
not  conspicuous 
F — Uneven 
Brittle 


2 . 1  Generally  in  cube-like  crys- 

2.2  tals.     Inferior      cleavage 
distinguishes  it  from  fluor- 
ite and  calcite.     In  basic 
igneous  rocks.  With  anal- 
cite,  stilbite. 


4.5 
5 


White 


C— Basal,    perfect, 

conspicuous 
F — Uneven 
Brittle 


2.3  Prism  faces  vertically  stri- 

2.4  ated.        In    fissures    and 
cavities  in  basic  igneous 
rocks.        With    natrolite, 
analcite,  datolite,  pecto- 
lite.  native  copper,  calcite. 


450 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

APATITE 
Ca6F(P04)3 


Hexagonal  Greasy 

C — Prismatic,  thick  tab-  Vitreous 

ular,  common,  some-  Translucent 

times      large      with      to  opaque 

rounded  edges 
M — Compact,       fibrous, 

nodular,  reniform 


Violet  red 
Brownish  red 
Red 


273 


Huebnerite 
MnWO4 

260 


Monoclinic  Resinous 

C — Long  fibrous,  bladed,  Submetallic 

stalky;  often  diver-  Translucent 

gent,   without  good      to  opaque 

terminations 
M — Compact,     lamellar, 

granular 


Brownish  red 


ANALCITE  (Zeolite) 
Na2Al2(Si03)4.2H20 

325 


Cubic  Vitreous  Reddish 

C — Tetragonal    trisocta-  Translucent      Brick  red 

hedrons,  cubes  to  opaque 
M — Granular,  compact 


Datolite 
Ca(B.OH)Si04 

283 


Monoclinic  Vitreous  Pink 

M^Compact,       fibrous,   Greasy  Red 

granular,  botryoidal  Dull  Red  violet 

Translucent 
to  opaque 


TITANITE  (Sphene) 
CaTiSi06 

323 


Monoclinic  Vitreous  Brownish  red 

C — Wedge-  or  envelope-  Greasy  Red 

shaped  when  dissem-  Transparent 
inated;    tabular    or     to  opaque 
prismatic   when   at- 
tached 
M — Compact,  lamellar 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


451 


Hardness  3  to  6 

Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

4.5        White                      C—  .Basal, 
5.          Reddish  white              feet 

imper-          3  .  1      Crystals  may  be  vertically 
3.2        striated   and  have   fused 

F — Conchoidal,  un- 
even 
Brittle 


appearance.  Color  often 
unevenly  distributed, — 
mottled  brown  and  green. 
In  crystalline  limestones, 
metalliferous  ore  deposits, 
igneous  rocks.  With 
quartz,  cassiterite,  fluor- 
ite,  wolframite,  magne- 
tite. 


4.5 
5.5 


Greenish  gray 


C — Clinopinacoidal, 
perfect,  c  o  n- 
spicuous 

Brittle 


6.7  Structure,  cleavage,  and 
7 . 3  specific  gravity  character- 
istic. In  quartz  veins. 
With  wolframite,  fluorite, 
pyrite,  scheelite,  galena, 
tetrahedrite. 


5.          White                      C—  None 
5.5        Reddish  white        F  —  Uneven,    c  o  n- 
choidal 
Brittle 

2  .  2      Good  crystals  common.    In 
2.3       fissures    and    cavities    in 
basic  igneous  rocks.  With 
apophyllite,       chabazite, 
natrolite,  datolite,  native 
copper,  epidote. 

5.         White                     C—  None 
6.5                                       F  —  Conchoidal,  un- 
even 
Brittle 

2  .  9      Compact  masses  often  with 
3.          brownish,    yellowish,    or 
whitish  streaks  and  spots. 
In  cracks  and  cavities  in 
basic  igneous  rocks.  With 
calcite,     epidote,     native 
copper,  zeolites. 

5.          White                      C  —  Prismatic,  con- 
5.5        Gray                              spicuous    part- 
ing often  noted 
F  —  Conchoidal 
Brittle 

3.4      With  feldspars,  pyroxenes, 
3  .  6        amphiboles,  chlorite, 
scapolite,  zircon. 

452 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Monazite                                    Monoclinic                           Resinous           Hyacinth  red 
C  —  Thick  tabular,  square  Vitreous            Brownish  red 
(Ce,La,Di)PC>4                               prismatic                      Translucent 
M  —  A  n  g  u  1  a  r,    rolled     to  opaque 
grains 

272 


SCAPOLITE  (Wernerite)        Tetragonal  Vitreous  Pink 

C — Prismatic  Greasy  Red  violet 

[  nNa4Al3Si9O24Cl  M — Compact,    granular,  Translucent  Brick  red 

fibrous,  columnar 


RHODONITE  (Pyroxene)       Triclinic  Vitreous  Brownish  red 

C — Tabular,     prismatic,  Dull  Flesh  red 

MnSiOa  rounded  edges,  often  Transparent     Rose  red 

large  to  opaque 
M — Compact,  cleavable, 
granular,       dissemi- 
309                                               nated  grains 

OPAL,  varieties  Amorphous  Vitreous  Red 

Fire  opal       M — Reniform,  botryoid-  Greasy  Brownish  red 

Opal  jasper  al,   stalactitic,   com-  Transparent 

SiO2.xH2O  pact  to  opaque 


232 


Streak — Uncolored,  white,  or  light  gray 


ORTHOCLASE  (Feldspar)      Monoclinic  Vitreous 

C — Prismatic,  thick  Pearly 

KAlSijOs  tabular,  twins;  Translucent 

often  large  to  opaque 


316 


M — Cleavable,  granular, 
disseminated 


Flesh  red 
Brick  red 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


453 


Hardness  3  to  6 


Cleavage 
Streak                  Fracture 
Tenacity 

i 

"v       Spe 

Gra 

cine          Characteristics  and 
vity                  Associates 

5.          White                       C  —  Basal                          4.9      Crystals  commonly  small, 
5.5                                       F  —  Conchoidal,  un-        5.3        highly    modified,    or    as 
even                                        rolled     grains     in     sand. 
Brittle                                           With    magnetite,    zircon, 
garnet,     gold,     chromite, 
diamond. 

5.          White                       C  —  Prismatic,     not 
6.                                              conspicuous 
F  —  Conchoidal 
Brittle 

2  .  6      Often  resembles  pink  fluor- 
2.8        ite  in  color,  but  cleavage 
less  distinct,  and  harder. 
In    metamorphic     rocks, 
especially  granular  lime- 
stones.    With  pyroxenes, 
apatite,    garnet,    titanite, 
biotite,  amphiboles. 

5.          White                      C  —  Prismatic,  basal 
6.          Reddish  white       F  —  Conchoidal,  un- 
even 
Tough,  when  mass- 
ive; crystals 
brittle 

3.4      May  be  stained  brown  to 
3  .  7        black  on  exposure.    Fow- 
leritej  variety  containing 
zinc.       With  franklinite, 
zincite,  willemite,  calcite, 
tetrahedrite. 

5.5        White  F — Conchoidal,  2.1      Structure      and      fracture 

6.  conspicuous  2.3        characteristic.     Fire  opal, 

Brittle  transparent  to  translucent 

and  red;  oped  jasper, 
greasy  and  opaque,  re- 
sembling jasper.  In  veins, 
cavities,  and  masses  of 
irregular  outline. 


Hardness  over  6 


6. 
6.5 


White 


C — Basal,  clinopin-        2 . 5      Characterized  by  rectangu- 


acoidal,  perfect, 
conspicuous — 
90° 

F — Conchoidal,  un- 
even 

Brittle 


2.6  lar  cleavage  and  absence 
of  twinning  striations.  In 
granitic  rocks.  With 
quartz,  other  feldspars, 
mica,  hornblende,  zircon. 


454 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Chondrodite 


[Mg(F,OH)]2Mg3(Si04)2 


286 


Monoclinic  Vitreous 

C — Small,   highly   modi-  Greasy 

fied,  rare  Translucent 
M — Rounded,      dissemi-     to  opaque 
nated   grains;    com- 
pact 


Brownish  red 
Dark  red 


RUTILE 

TiO2  or  TiTiO4 


224 


Tetragonal  Adamantine 

C — Prismatic,    vertically  Submetallic 
striated;       twinned,  Translucent 
yielding  knee-shaped    to  opaque 
or  rosette  forms 
M — Compact,      dissemi- 
nated 


Dark  red 
Brownish  red 


CASSITERITE 

SnO2  or  SnSnO4 


Tetragonal  Adamantine 

C — T  hick  prismatic;  Resinous 

knee-shaped      twins  Dull 

quite  common  Translucent 

M — Compact,  reniform,  to  opaque 

botryoidal,   rounded 

pebbles,    often  with 

internal,    radial 

fi  b  r  o  u  s  structure, 

wood  tin 


Brownish  red 
Yellowish  red 


ANDALUS1TE 
Al2SiO6 


Orthorhombic  Vitreous  Pink 

C — Prismatic,   rough,  Dull  Rose  red 

nearly  square,  often  Translucent      Red  violet 
large    and    without     opaque 
terminations 
M — Columnar,     fibrous, 
granular,       dissemi- 
nated 


281 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


455 


Hardness  over  6 


lard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  arid 
Associates 

6. 
6.5 


White 


C— Basal 

F — Conchbidal,  un- 
even 
Brittle 


3 . 1      Associates  important. 

3 . 3  Chiefly  in  crystalline  lime- 
stones and  dolomites. 
With  spinel,  vesuvianitc, 
pyroxenes,  magnetite, 
mica. 


Gray 

Yellowish  white 
Brownish  white 


C — Prismatic,  .  py- 
ramidal, not 
conspicuous 

F — Uneven 

Brittle 


4 . 2  Not  as  heavy  as  cassiterite. 

4.3  Often    as    fine    hair-like 
inclusions.     Widely     dis- 
tributed.    With     quartz, 
feldspar,  hematite,  ilmen- 
ite,  chlorite. 


6.  White  C — Indistinct  C.8      Distinguished  by  high  spe- 

7.  Yellowish  white     F — Uneven  7 .          cine    gravity.     In    veins 
Brownish  white     Brittle  cutting    granite,    gneiss; 

in  alluvial  deposits  as 
stream  tin.  With  quartz, 
wolframite,  scheelite, 
arsenopyrite,  tourmaline, 
fluorite,  mica,  chlorite. 


6. 
7.5 


White 


C — Prismatic  3 . 1      Due  to  alteration,  surface 

F — Uneven  3.2        may     be     covered     with 

Brittle  scales  of  mica  and,  hence, 

is  softer.  In  metamorphic 
rocks  often  as  rounded  or 
knotty  projections.  With 
cyanite,  sillimanite,  gar- 
net, tourmaline. 


456 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

GARNET,  varieties 


Cubic 


Vitreous 


Rose  red 


Grossularite  C — Dodecahedrons,     te-  Transparent     Ruby  red 

IVRa"'            Pyrope  tragonal   trisoctahe-     to  opaque       Brownish  red 

(8104)3          Spessartite  drons,    alone   or   in                            Dark  red 

R"  =  Ca,         Almandite  combination 

Fe,Mg           Andradile  M — Granular,    compact, 

R'"  =  Al,Fe  lamellar,       dissemi- 
nated, sand 


290 


QUARTZ, 

Phanerocrystal- 

Hexagonal 

Vitreous 

Red  violet 

line  varieties 

C  —  Prismatic,      horizon- 

Greasy 

Rose  red 

SiO2 

Amethyst 

tally  striated,  com- 

Transparent 

Brick  red 

Rose  quartz 

mon 

to  opaque 

Brownish  red 

Aventuririe 

M  —  Compact,  granular 

Ferruginous 

220 


Cryptocrystalline 

Hexagonal 

Waxy 

Bright  red 

varieties 

C  —  Never  in  crystals 

Vitreous 

Dark  red 

Carnelian 

M  —  Banded,  spotted, 

Translucent 

Brownish  red 

Agate 

compact 

to  opaque 

Sard 

Jasper 

Heliotrope 

Clastic  varieties 

Hexagonal 

Vitreous 

Red 

Sand 

Loose   or   strongly   con- 

Dull 

Brownish  red 

Sandstone 

solidated   grains   or 

Translucent 

Purplish  red 

Quartzite 

fragments 

to  opaque 

2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


4.1 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.5        White                      C  —  Dodecahedral,          3.4      Grossularite,  in  crystalline 

7.6        Gray                              indistinct                  4.3        limestones  and  dolomites, 

F — Conchoidal,  un- 
even 
Brittle 


with  wollastonite,  vesuvi- 
anite,  diopside,  scapolite; 
pyrope,  rounded  grains,  in 
serpentine;  spessartiie,  in 
granitic  rocks,  with  topaz, 
tourmaline,  quartz,  ortho- 
clase;  almandite,  with 
mica,  staurolite,  andalus- 
ite,  cyanite;  andradite, 
with  magnetite,  epidotc, 
feldspar,  nephelite,  leu- 
cite. 


7. 


White 
Reddish  white 


C — Indistinct 
F — Conchoidal, 
conspicuous 
Brittle 


2.6  Characteristic  Conchoidal 
fracture  and  glassy  luster. 
Amethyst,  usually  in  crys- 
tals, purple  or  blue  violet; 
rose  quartz,  usually  mass- 
ive, pink  to  rose  red; 
aventurine,  massive  and 
glistening,  due  to  in- 
cluded scales;  ferruginous 
quartz,  colored  by  iron 
oxide. 


White 
Reddish  white 


C — Indistinct 
F — Conchoidal, 
conspicuous 
Brittle  to  tough 


2.6  Not  as  glassy  as  phanero- 
crystalline  varieties.  Car- 
nelian,  jasper,  uniform  in 
color;  agate,  sardonyx, 
banded;  heliotrope,  spot- 
ted. To  distinguish,  see 
reference. 


White  C — Indistinct  2.6      Pigment    is    usually    fer- 

Reddish  white       F — Uneven  ruginous    matter.     Sand, 

Brittle  to  tough  loose,    unconsolidated 

grains;  sandstone,  con- 
solidated sand;  quartzite, 
metamorphosed  s  a  n  d- 
stone. 


458 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

TOURMALINE,  variety 
Rubellite 

M9'Al3(B.OH)2Si4O19 
M'  =  Na,K,Li,Mg,Fe 


284 


Hexagonal  Vitreous  Pink 

C — Prismatic,    often  Transparent     Rose  red 

vertically      striated,     to  trans-          Ruby  red 

rarely      with     good     lucent 

terminations 
M — Divergent,  columnar, 

compact 


ZIRCON 
ZrSiO4 

226 


Tetragonal  Adamantine 

C — Prismatic,  pyramidal,  Vitreous 

small,  well  developed  Resinous 
M — Irregular  lumps,          Transparent 

grains  .        to  opaque 


Brownish  red 
Dark  red 


SPINEL,  varieties 

Balas 

R"(R'"O2)2      Ruby 
R"  =  Mg,Fe, 

Mn  Rubicelle 

R"'  =  Al,Fe  Almandine 


Cubic  Vitreous  Deep  red 

C — Octahedral,  twins,  Splendent  Rose  red 

small  Transparent  Orange  red 

M — Rounded    grains,     to  trans-  Bluish  red 

small  pebbles  lucent 


267 


CORUNDUM,  varieties 

Ruby 
A12O3  Oriental 

amethyst 
Common 


Hexagonal  Vitreous  Pink 

C — Prismatic,       tabular,  Transparent     Red 

pyramidal,  rhombo-     to  trans-          Red  violet 

hedral,      rough      or     lucent 

rounded    barrel- 

shaped 
M — Compact,    granular, 

lamellar 


228 


2.  PINK,  RED,  OR  RED  VIOLET  IN  COLOR 


459 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

7. 
7.5 

White                      C  —  None                      x  2.9      Spherical  triangular  cross- 
F  —  Conchoidal,  un-        3  .  2        section.    Often  with  zonal 

even 
Brittle 


distribution  of  color — red, 
green,  colorless.  F  r  e- 
quently  as  long,  diverg- 
ent, columnar  masses  im- 
bedded in  lepidolite. 


7.5       White 


C — Indistinct  4.4      Often    in    the    more    acid 

F — Uneven  4.8        igneous     rocks — granites, 

Brittle  syenites ;  alluvial  deposits, 

with  gold,  spinel,  corun- 
dum, garnet.  Hyacinth, 
clear  and  transparent. 


8. 


White 


C — Octahedral,  in- 
distinct 
F — Conchoidal 
Brittle 


3 . 5  Balas  spinel,  rose  red ;  ruby 
4.1  spinel,  deep  red;  rubicelle, 
yellow  to  orange  red; 
almandine,  bluish  red. 
Usually  in  precious  stone 
placers,  with  zircon,  gar- 
net, magnetite ;  more 
rarely  as  contact  mineral 
in  crystalline  limestones. 


9. 


White 


C — None.  Nearly 
rectangular 
basal  and  rhom- 
bohedral  part- 
ings, conspicu- 
ous; often  stri- 
ated 

F — Conchoidal 
Brittle  to  tough 


3 . 9  When  massive  often  multi- 
4.1  colored — blue,  green, 
gray.  Ruby,  transparent 
red ;  oriental  amethyst, 
violet.  In  limestones, 
granites;  schists,  perido- 
tites,  alluvial  deposits. 
With  magnetite,  hema- 
tite, nephelite,  mica, 
spinel. 


460 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Blue,  green,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CHLORITE  (Prochlorite,        Monoclinic 

clinochlorite)   C — Tabular,  six-sided, 
H8Mg5Al2Si3Oi8  ?  often  bent  and 

twisted 

M — Foliated,  scaly, 
g  anular,  earthy 


Pearly  Grass  green 

Vitreous  Brownish 

Dull  green 

Translucent  Blackish 

to  opaque  green 


297 


CHRYSOCOLLA 

H2CuSi04.H20 


Amorphous  ?  Vitreous 

M — Compact,    reniform,  Greasy 

incrustations,  seams,  Dull 

stains,  earthy 


Green 
Greenish 
blue 

Translucent      Blue 
to  opaque 


293 

Garnierite 
H2(Ni,Mg)Si04 

Amorphous  ? 
M  —  Compact, 
earthy 

Dull 
reniform,   Greasy 
Opaque 

Pale  green 
Apple  green 
Emerald 
green 

300 

Chalcanthite  (Blue  vitriol) 
CuS04.5H20 

Triclinic 
C  —  Tabular,  small,  rare, 
M  —  Crusts,  reniform, 
stalactitic,  powdery 

Vitreous 
Dull 
Translucent 

Deep  blue 
Sky  blue 
Greenish  blue 

Brochantite 
CuSO4.3Cu(OH)2 

Orthorhombic 
C  —  Prismatic,  acicular, 
vertically  striated 
M  —  Reniform,  fibrous, 
drusy  crusts 

Vitreous            Emerald 
Pearly                 green 
Transparent     Blackish 
to  trans-           green 
lucent 

263 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


461 


1. 
2.5 


Pale  green 


Hardness  1  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Basal,  perfect; 
when  foliated, 
conspicuous 
F — Scaly,  earthy 
Tough  to  brittle 


2.6  Laminae  are  flexible  but 
3.  inelastic,  with  slightly 
soapy  feel.  Common  in 
schists  and  serpentine. 
With  magnetite,  garnet, 
diopside,  magnesite. 
Often  as  a  scaly  or  dusty 
coating  on  other  minerals. 
Pseudomorphous  after 
garnet. 


2.          Pale  green  F — Conchoidal  2.        Usually      recognized      by 

4.          Pale  blue  Brittle  2.2        enamel-like     appearance, 

conchoidal  fracture,  and 
n  o  n-fibrous  structure. 
When  impure  brownish 
or  blackish.  With  cop- 
per minerals — malachite, 
azurite,  chalcopyrite. 


2.  Pale  green  C — None  2 . 3      Often    as    rounded,     pea- 

3.  F — Conchoidal,  2 . 8        shaped  masses  with  varn- 

earthy  ish-like       surfaces       and 

Brittle  earthy     interior.     F  r  e- 

quently  adheres  to 
tongue.  With  olivine, 
serpentine,  chromite,  talc. 


2.5       Light  blue  C — Indistinct  2.1      Disagreeable  metallic  taste. 

F — Conchoidal  2 . 3        Oxidation  product  of  cop- 

Brittle  per     sulphide     minerals. 

With  chalcopyrite,  born- 
itc,    melanterite,    pyrite. 


3.5       Light  green 


C — Brachypina- 

coidal 
F — Uneven 
Brittle 


3.8  Not  as  common  as  mala- 

3.9  chite.     Secondary  copper 
mineral.    With  malachite, 
azurite,    cuprite,    chalco- 
pyrite,  limonite. 


402 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Blue,  green,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

AZURITE 

2CuCO3.Cu(OH)2 


252 


Monoclinic  Vitreous 

C — Short  prismatic,  tab-  Dull 

ular,  often  in  spher-  Translucent 

ical  aggregates  to  opaque 

M — Fibrous;  botryoidal, 

with  velvety  or 

radial  structure; 

earthy,  crusts 


Azure  blue 
Dark  blue 


MALACHITE 

CuCO3.Cu(OH)2 


252 


Monoclinic  Silky 

C — Acicular,  often  in  Adamantine 

groups  or  tufts  Dull 

M — Fibrous;  stalactitic,  Translucent 

botryoidal,    with     to  opaque 

smooth  surface  and 

internal    banded    or 

radial  fibrous  struc- 
ture; velvety  crusts, 

earthy 


Emerald 
green 

Grass  green 
Dark  green 


PYROMORPHITE 

Pb6Cl(P04)3 

275 


Hexagonal  Greasy  Dark  green 

C — Prismatic,  thick  tab-  Adamantine  Emerald 
ular,    rounded    and  Translucent        green 

barrel-shaped  to  opaque  Yellowish 

M — Globular,    reniform,  green 

disseminated,  crusts 


Lazurite  (Lapis  lazuli) 

(Na2,Ca)2Al2[Al(NaS04, 
NaS3,Cl)](Si04)3 
303 


Cubic  Vitreous  Azure  blue 

C — Dodecahedrons,  rare  Translucent  Violet  blue 

M — Compact,     irregular     to  opaque  Greenish 
grains  blue 


HORNBLENDE  (Amphi-       Monoclinic  Vitreous 

bole)  C — Long  prismatic,  prism  Silky 

"Silicate  of  Ca,  Mg,  Fe,  Al,  angle     124°;     often  Translucent 

etc.  with  rhombohedral-     to  opaque 

like  terminations 
M — Bladed,  fibrous, 

granular,  compact 
312 


Blackish 
green 
Dark  green 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


463 


Hardness  1  to  6 


Hard- 
btreak 
ness 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.6        Blue                         C  —  Domatic                    3.7      Common  alteration  prod- 
4.                                         F  —  Conchoidal               3.8        uct    of   copper   minerals. 
Brittle                                           With  malachite,  cuprite, 

native  copper,  chalcocite, 
chalcopyrite,  b  o  r  n  i  t  e. 
Pseudomorphous  a.f  t  e  r 
cuprite,  tetrahedrite. 
Alters  to  malachite. 


3.6       Light  green  C — Basal,  pi na-  3.7      Very    common    alteration 

4.  coidal  4 . 1        product   of   copper   min- 

F — Conchoidal,  erals.     With  azurite,  cu- 

splintery  prite,  native  copper,  ehal- 

Brittle  cocite,  chalcopyrite,  born- 

ite.  Pseudomorphous 

after  cuprite,  azurite, 
native  copper.  Surface 
may  be  almost  black,  due 
to  the  oxide,  melaconite. 


3.5 

4. 


Yellow 
Greenish  yellow 


C— None 

F — Conchoidal,  un- 
even 
Brittle 


6.5      Alteration  product  of  lead 

7.1        minerals.     With     galena, 

cerussite,  barite,  limonite. 


6. 
6.6 


Pale  blue 


C — Dodecahedral, 

distinct 
F — Uneven 
Brittle 


2.4  Always  blue  and  contains 
disseminated  p  y  r  i  t  e. 
Occurs  as  contact  mineral 
in  crystalline  limestone. 


Grayish  green 
Grayish  brown 
Yellowish 


C — Prismatic,  per- 
fect, often  con- 
spicuous— 124° 

Brittle 


2 . 9  Simple,  pseudohexagonal 
3.3  crystals,  and  cleavage — 
124° — important.  In 
nearly  all  types  of  igneous 
rocks.  With  quartz,  feld- 
spar, pyroxene,  chlorite, 
calcite. 


464 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Blue,  green,  brown,  or  yellow 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

• 
Color 

AUGITE  (Pyroxene)  Monoclinic 

C — Short,  prismatic, 

Silicate  of  Ca,  Mg,  Fe,  Al,  thick  columnar; 

etc.  prism  angle  87° 

M — Compact,  granular, 
disseminated 


Vitreous  Blackish 
Submetallic        green 

Translucent  Leek  green 
to  opaque 


307 


Turquois 

A12(OH)3PO4.H2O 
276 


Triclinic  ?  Waxy  Sky  blue 

C — Small,  rare  Dull  Bluish  green 

M — Reniform,  stalactitic,  Opaque  to         Apple  green 

disseminated,  round-    translucent 

ed  pebbles 


Streak — Uncolored,  white,  or  light  gray 


Asbestos,  variety 
Chrysotile 
H4Mg3Si209 


Orthorhombic  ?  Silky  Light  green 

M — Fibrous,    coarse    or  Silky  metallic  Olive  green 
fine;  felted  Opaque 


variety  Monoclinic  ?                         Silky 

Amphibole  M — Fibrous,     coarse    or  Opaque 

Silicate  of  Ca,  Mg,  Fe,  Al,  fine;  felted 
311                              etc. 


Greenish 


TALC,  varieties  Monoclinic  Pearly  Pale  green 

Foliated  C — Thin  tabular,   indis-  Greasy  Apple  green 

Soapstone  or  steatite          tinct  Opaque  to         Dark  green 

H2Mg3Si4Oi2  M — Foliated,      globular,     transparent 

granular,     compact, 
fibrous 


299 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


465 


Hardness  1  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 

Associates 

5.          Pale  green               C  —  Prismatic,   per-        3  .  2      Crystals,     usually     eight 
6.          Grayish  green               feet,    conspicu-        3  .  6       sided,   more  rarely  four- 
ous  —  87°                                sided;      pseudotetragonal 
Brittle                                           with  prism  angles  of  87° 

and  93°.  Cleavage  less 
distinct  than  on  horn- 
blende. Common  in  basic 
eruptive  rocks  and  crys- 
talline limestones. 


6.          Pale  green  F — Conchoidal  2 . 6      Secondary    mineral,    corn- 

Brittle  2 . 8        mon  in  thin  veins,  crusts, 

or  coatings.  With  limon- 
ite,  quartz,  feldspar, 
kaolin. 


Hardness  1  to  3 


1.          White 
2.5 


F — Fibrous 
Flexible 


1.  Delicate,  fine,  parallel- 
2 . 5  flexible  fibers  perpendicu- 
lar to  walls,  easily  separ- 
able, called  short  fibered 
asbestos;  compare  below. 
In  veins  or  seams  in  com- 
pact serpentine. 


1.          White 
2.5 


F — Fibrous 
Flexible 


1 .        Long  fibered  asbestos,  par- 
2.5        allel,    flexible    fi  b  e  r  s. 

Fibers   parallel  to  walls. 

Compare  above. 


1.          White 
2.5 


C — Basal,  conspic- 
uous on  foliated 
masses 

F — Uneven 

Sectile,  laminae  flex- 
ible 


2 . 6  Greasy  or  soapy  feel.  Foli- 
2.8  ated,  easily  separable,  in- 
elastic folia  or  plates, 
H  =  1 ;  Soapstone  or  stea- 
tite, coarse  to  fine  granu- 
lar, more  or  less  impure, 
H  =  1.5  -  2.5.  With  ser- 
pentine, dolomite,  mag- 
nesite,  actinolite. 


466  B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CHLORITE  (Prochlorite,        Monoclinic  Pearly  Grass  green 

clinochlorite)   C — Tabular,  six-s  i  d  e  d,   Vitreous  Brownish 
H8Mg5Al2Si3Oi8  ?                         often  bent,  twisted      Dull  green 

M — Foliated,  scaly,  gran-  Translucent  Blackish 
ular,  earthy                    to  opaque         green 


297 

Melanterite  (Copperas) 
FeSO4.7H2O 

Monoclinic                           Vitreous            Green 
C—  Rare                                Dull                   Yellowish 
M  —  Capillary,      fibrous,  Transparent       green 
stalactitic,      concre-     to  trans- 
tionary,  powder             lucent 

266 


CHRYSOCOLLA 

Amorphous  ? 

Vitreous 

Green 

M  —  Compact,    reniform, 

Greasy 

Greenish 

H2CuSi04.H20 

incrustations,  seams, 

Dull 

blue 

stains,  earthy 

Translucent 

Blue 

to  opaque 

293 


Garnierite 

H2(Ni,Mg)SiO4 


Amorphous  ?  Dull 

M — Compact,   reniform,  Greasy 
earthy  Opaque 


Pale  green 
Apple  green 
Emerald 
green 


300 


Actinolite  (Amphibole) 
Ca(Mg,  Fe)3(Si03)4 


Monoclinic  Vitreous  Grass  green 

C — Fine,  acicular  Silky  Grayish 

M — Interwoven    fibrous  Translucent       green 

aggregates,     radiat-     to  opaque 

ing  masses 


311 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


467 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

1.          White                      C  —  Basal,  conspic-        2.G      Laminae    flexible    but    in- 
2.5        Greenish  white             uous,  when               3  .          elastic,    with  slightly 

foliated 

F — Scaly,  earthy 
Tough  to  brittle 


soapy  feel.  Common  in 
schists  and  serpentine. 
With  magnetite,  mag- 
nesite,  garnet,  diopside. 
Often  as  scaly  or  dusty 
coating  on  other  minerals. 
Pseudomorphous  after 
garnet. 


White 


C — Basal,  not  con- 
spicuous 

F — Conchoidal, 
earthy 

Brittle 


1.8  On   exposure   loses    water 

1.9  and  crumbles  to  powder. 
Sweet,    astringent    taste, 
somewhat  metallic.    Oxi- 
dation   product    of    iron 
sulphide    minerals — mar- 
casite,    pyrite,    chalcopy- 
rite,  pyrrhotite. 


2.  \Vhite  F — Conchoidal  2.        Usually      recognized      by 

3.  Greenish  white      Brittle  2 . 2        enamel-like     appearance, 
Bluish  white  conchoidal  fracture,   and 

n  o  n-fibrous  structure. 
When  impure  brownish  or 
blackish.  With  copper 
mineral  s — malachite, 
azurite,  chalcopyrite;  also 
limonite. 

2.  White  C — None  2.3      Often    as    rounded,    pea- 

3.  Greenish  white      F — Conchoidal,  2.8       shaped  masses,  with  varn- 

earthy  ish-like  surfaces  and 
Brittle                                           earthy  interior.     May  ad- 
here    to     tongue.     With 
olivine,  serpentine,  chro- 
mite,  talc. 


White 
Greenish  white 


C— Fibrous 
Brittle 


2.9  Masses  of  delicate,  inter- 
3.2  woven  fibers — actinolite 
schist.  A  pale  grayish 
green,  highly  ferruginous 
variety  (ffrunerite,  Fet- 
(SiO3)4)  associated  with 
quartz  and  magnetite  is 
termed  magnetite-gruner- 
ite  schist. 


468 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Chalcanthite  (Blue  vitriol)      Triclinic  Vitreous  Deep  blue 

C— Tabular,  small,  rare     Dull  Sky  blue 

CuSO4.5H2O  M — Crusts,  reniform,         Translucent      Greenish  blue 

stalactitic,  fibrous, 
powdery 
266 


BIOTITE  (Mica)  Monoclinic  Pearly  Brownish 

C — Tabular,     hexagonal  Submetallic        green 
(K,H)2(Mg,Fe)2(Al,Fe)2-  or  rhombohedral          Transparent     Blackish 


(Si04)i 


294 


habit 
M — Plates,  disseminated 


to  opaque         green 


BARITE  (Heavy  spar) 
BaSO, 


Orthorhombic  Vitreous  Bluish 

C — Tabular,  prismatic,      Pearly  Greenish 

crested  divergent         Transparent 

groups,  common  to  opaque 

M — Compact,  lamellar, 

fibrous,  cleavable, 

reniform 


256 


CALCITE 
CaCOs 
242 


Hexagonal     '  Vitreous       .     Sky  blue 

M — Cleavable,  granular,   Dull  Deep  blue 

fibrous,  compact          Transparent      Greenish 

to  nearly 

opaque 


Streak — Uncolored,  white,  or  light  gray 


ANHYDRITE 

CaSO4 

254 


Orthorhombic  Vitreous  Bluish 

C — Thick   tabular,   pris-  Pearly  Grayish  blue 

matic,  rare  Translucent      Blue 

M — Granular,    compact,  to  opaque 

fibrous,        lamellar, 

cleavable,  reniform 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


469 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

2.5       White                      C  —  Indistinct                 2.1      Disagreeable  m  e  t  a  1  1  i  c 
Bluish  white           F  —  Conchoidal,              2  .  3        taste.    Oxidation  product 
earthy                                    of  copper  sulphide  min- 
Brittle                                           erals.     With  chalcopyrite, 
bornite,  melanterite,  py- 
rite. 

2.5       White 
3.          Grayish 


C — Basal,    perfect, 
conspicuous 

Tough,    laminae  of 
fresh  biotite 
very  elastic 


2 . 7  Easily  recognized  by  struc- 
3 . 2  ture,  highly  perfect  cleav- 
age, and  elasticity.  Im- 
portant constituent  of 
many  igneous  and  meta- 
morphic  rocks — granite, 
syenite,  gneiss. 


2.5 
3. 


White 


C — Basal,  pris-  4.3      Characterized    by    rather 

matic,  con-  4.7       high  specific  gravity  and 

spicuous  cleavages.     In  metallifer- 

F — Uneven  ous   veins;   pockets,   len- 

Brittle  ticular    masses    in    lime- 

stone. With  galena, 
sphalerite,  chlorite,  chal- 
copyrite; manganese  and 
iron  minerals. 


3. 


White 


C — Rhombohedral 
perfect,  con- 
spicuous 

F — Conchoidal 

Brittle 


2.7  Rhombohedral  cleavag*e 
generally  characteristic. 
Cleavages  often  show 
striations. 


Hardness  3  to  6 


3. 
3.6 


White 


C — Pinacoidal,  per- 
fect, 3  direc- 
tions at  90° 

F— Conchoidal 

Brittle 


2 . 8  Pseudocubical  cleavage, 
3 .  *  sometimes  noted.  Gran- 
ular varieties  resemble 
marble.  Not  as  heavy  as 
celestite  or  barite.  In 
limestone,  shale.  With 
halite,  gypsum. 


470 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CELESTITE 


255 


Orthorhombic  Vitreous 

C  —  Tabular,     prismatic,  Pearly 

common;  pyramidal 
M  —  Compact,  cleavable, 

fibrous,  granular, 

reniform 


Sky  blue 
Blue 
Transparent     Greenish 

to  trans- 

lucent 


BARITE  (Heavy  spar) 
BaS04 


Orthorhombic  Vitreous 

C  —  Tabular,     prismatic,  Pearly 

crested        divergent  Transparent 

groups,  common  to  trans- 

M  —  Compact,    lamellar,     lucent 

fibrous,       cleavable, 

reniform 


Bluish 
Greenish 


256 


CHRYSOCOLLA 

Amorphous  ? 

Vitreous 

Blue 

M  —  Compact,    reniform, 

Greasy 

Bluish  green 

H2CuSi04.H20 

incrustations,  seams, 

Dull 

Green 

stains,  earthy 

Translucent 

to  opaque 

293 

SERPENTINE 
H4Mg3Si209 

Orthorhombic  ? 
C  —  Unknown 
M  —  Compact,  columnar, 
fibrous,  lamellar, 
granular 

Greasy 
Waxy 
Translucent 
to  opaque 

Light  green 
Olive  green 
Yellowish 
green 
Blackish 

green 

297 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


471 


Hardness  3  to  6 


Hard- 
ness 

'  Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.          White                      C—  Basal,  pris-               3.9      Heavier  than  calcitc,  anhj-. 

3.6                                              matic,  con-               4.          drite;  lighter  than  barite. 

spicuous                                 In  limestones,  dolomites, 

F  —  Uneven                                  shale  s.     With  sulphur, 

Brittle                                           gypsum,  aragonite,  halite, 

galena,  sphalerite. 

3. 
3.5 


White 


C — Basal,  pris-  4.3      Characterized    by    rather 

matic,  con-  4.7        high  specific  gravity  and 

spicuous  cleavages.     In  metallifer- 

F — Uneven  ous   veins;   pockets,   len- 

Brittle  ticular    masses    in    lime- 

stone. With  galena, 
sphalerite,  chalcopyrite ; 
manganese  and  iron  min- 
erals. 


3.  White  F — Conchoidal  2.        Usually      recognized      by 

4.  Greenish  white      Brittle  2.2        enamel-like     appearance, 
Bluish  white  conchoidal  fracture,   and 

n  o  n-fibrous  structure. 
When  impure  brownish  or 
blackish.  With  copper 
mineral  s — malachite, 
azurite,  chalcopyrite;  also 
limonite. 


White 


F — Conchoidal,  2.5  Smooth  and  greasy  feel, 

splintery  2.8  Often  spotted,  clouded, 

Brittle  and  multi-colored.  Some- 

times crossed  by  seams  of 
asbestos  (ch^sotile). 
Verd-antique,  massive, 
green  and  mixed  with  cal- 
cite,  dolomite,  or  mag- 
nesite;  takes  an  excellent 
polish.  WTith  magnesite, 
chromite,  garnierite,  py- 
rope,  platinum. 


472 


B.     MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Wavellite 

(A1.OH)3(PO4)2.5H2O 

276 


Orthorhombic  Vitreous  Green 

C — Capillary,  small  Translucent      Bluish  green 

M — Crusts,   globular  or  Blue 

hemispherical,  with 
radial  fibrous  struc- 
ture 


PYROMORPHITE 

Pb6Cl(P04)3 

275 


Hexagonal  Greasy 

C — Prismatic,  thick  tab-  Adamantine 

ular,    rounded    and  Translucent 

barrel-shaped;  to  opaque 

acicular 
M — Globular,    reniform, 

disseminated,  crusts 


Dark  green 
Emerald 

green 
Yellowish 

green 


FLUORITE  (Fluor  spar) 
CaF2 


Cubic  Vitreous 

C — Cubes,  alone  or  modi    Transparent 

fied,  well  developed,     to  nearly 

common;       penetra-     opaque 

tion  twins 
M — Cleavable,  granular, 

fibrous 


Greenish 
Bluish  green 
Blue  violet 


CYANITE  (Disthene,  kyan-  Triclinic  Vitreous 

ite)   C — Long,    bladed,    with-  Translucent 
Al2SiO6  out    good    termina-     to  trans- 

t  i  o  n  s;   sometimes     parent 
curved  and  radially 
grouped 

M — Coarsely  bladed,  col- 
umnar, fibrous 


282 
APATITE 


Sky  blue 
Greenish  blue 
Bluish  white 


Hexagonal 


Greasy 


Grass  green 


C — Prismatic,  thick,  tab-  Vitreous  Brownish 

ular,  common,  some-  Translucent  green 

times      large      with     to  opaque  Bluish  green 

rounded  edges  Blue  violet 

M — Compact,  fibrous, 
nodular,  reniform 


273 


3.     GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


473 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.5        White                      C  —  Pinacoidal,  do-        2.3      Secondary  mineral  occur- 
4.                                                matic                         2.4        ring  on  surfaces  of  rocks 
F  —  Conchoidal,  un-                    or  minerals,  as  crystalline 
even,  fibrous                         crusts    with    pronounced 
Brittle                                         radial,  fibrous  structure. 

3.5 

4. 


White 
Yellowish  white 


C — None 

F — Conchoidal,  un- 
even 
Brittle 


6.5      Common  alteration  prod- 
7.1        uct     of     lead     minerals. 

With    galena,     cerussite, 

barite,  limonite. 


White 


C — Octahedral, 
perfect,  con- 
spicuous 

Brittle 


3.         May     show     fluorescence. 

3 . 2  Easily  recognized  by  crys- 
tal form,  octahedral  cleav- 
age, and  hardness.  Com- 
mon gangue  of  metallic 
ores — galena,  sphalerite, 
cassiterite;  also  with  cal- 
cite,  barite. 


White 


C — Pinacoidal,  per- 
fect, con- 
spicuous 

Brittle 


3.5  Color  irregularly  distribu- 
3.7  ted,  frequently  with 
lighter  longitudinal  mar- 
gins. Hardness  varies 
with  direction,  4-5  par- 
allel to  long  direction,  6-7 
at  right  angles  thereto. 
In  gneiss,  mica  schist. 
With  staurolite,  garnet, 
corundum. 


4.5 
5. 


White 


C — Basal,  imper- 
fect 

F — Conchoidal,  un- 
even 

Brittle 


3 . 1  Crystals  may  be  vertically 

3.2  striated   and  have  fused 
appearance.     Color  often 
unevenly       distributed — 
brownish  spots.     In  crys- 
talline limestones;  metal- 
liferous ore  deposits ;  igne- 
ous rocks.     With  quartz, 
cassiterite,    fluorite,   wol- 
framite. 


474 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

SMITHSONITE 

ZnC03 

247 


Hexagonal  Vitreous  Green 

C — Small,      usually      as  Dull  Grayish  green 

druses  or  crusts  Translucent  Greenish  blue 

M — Botryoidal,  stalactit-  Blue 

ic,  granular,  fibrous, 

compact 


Lazurite  (Lapis  lazuli)  Cubic  Vitreous  Azure  blue 

C — Dodecahedrons,  rare    Translucent      Violet  blue 
(Na2,Ca)2Al2[Al(NaSO4,       M — Compact,     irregular     to  opaque       Greenish  blue 

NaS3,Cl)](SiO4)3  grains 

303 


Datolite 

Ca(B.OH)SiO4 


Monoclinic  Vitreous  Pale  green 

C — Prismatic,  pyramidal,  Greasy  Olive  green 

tabular,  highly  mod-  Dull 

ified  Transparent 

M — Compact,  fibrous,  to  opaque 

granular,  botryoidal 


283 


TITANITE  (Sphene) 
CaTiSiO6 

323 


Monoclinic  Vitreous  Green 

C — Wedge-  or  envelope-  Greasy  Yellowish 

shaped     when     dis-  Transparent       green 

seminated;     tabular     to  trans- 

or    prismatic    when     lucent 

attached 
M — Compact,  lamellar 


Sodalite 

Na4Al2(AlCl)(Si04); 

303 


Cubic  Vitreous  Lavender  blue 

C — Dodecahedrons  Greasy  Sky  blue 

M — Compact,      dissemi-  Transparent  Dark  blue 

nated  grains,  to  trans-  Greenish 

nodular  lucent 


NEPHELITE  (Nepheline,       Hexagonal  .  Greasy  Grayish  green 

elseolite)  C — Short  prismatic,  tab-  Vitreous  Brownish 

(Na,K)8Al8Si9O34  ular  Transparent  green 

M — Compact,      dissemi-     to  opaque  Grayish  blue 
301                                              nated  grains 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


475 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 

Associates 

5.          White                       C  —  Rhombohedral,        4.1      With    zinc    minerals,     es- 
Gray                              not    often    ob-        4.5        pecially  sphalerite,  hemi- 
served                                    morphite. 
F  —  JJneven, 
splintery 
Brittle 

6.         White 

5.5        Bluish  white 


5.          White 
6.5 


C — Dodecahedral, 

imperfect 
F — Uneven 
Brittle 


2.4  Always  blue  and  contains 
disseminated  p  y  r  i  t  e. 
Occurs  as  contact  rnin- 
eral  in  crystalline  lime- 
stone. 


C — None 

F — Conchoidal,  un- 
even 
Brittle 


2 . 9  Crystals  glassy  and  usually 
3 .  well  developed.  Compact 
masses  often  with  brown- 
ish, yellowish,  reddish 
streaks  •  and  spots.  In 
cracks  and  cavities  in 
basic  igneous  rocks.  With 
calcite,  native  copper, 
magnetite,  zeolites. 


6.          White 
5.5       Grayish 


C  —  Prismatic,  con- 
spicuous  part- 
ing often  noted 

F  —  Conchoidal 

Brittle 


3.4      With  feldspars,  pyroxenes, 
3 . 6        amphiboles,    chlorite, 
scapolite,  zircon. 


White 


C — Dodecahedral 
F — Conchoidal,  un- 
even 
Brittle 


2.2  Commonly  massive  and 
2.4  blue  in  color.  Recog- 
nized by  associates — 
nephelite,  cancrinite,  leu- 
cite,  feldspar,  zircon;  not 
with  quartz. 


White 


C — Indistinct 
F — Conchoidal,  un- 
even 
Brittle 


2.6  Greasy  luster  and  asso- 
ciates important.  With 
feldspar,  cancrinite,  bio- 
tite,  sodalite,  zircon,  leu- 
cite;  not  with  quartz. 


476 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

SCAPOLITE  (Wernerite)        Tetragonal 

C — Thick  prismatic, 
/  nNa4Al3Si9O24Cl 


Vitreous  Grayish  green 

Greasy  Bluish 

coarse,  often  large       Translucent 
M — Compact,    granular,     to  opaque 
fibrous,  columnar 


322 


Actinolite 


Ca(Mg,Fe)3(Si03)4 


310 


Monoclinic  Vitreous  Light  green 

C — Bladed,  without  ter-  Silky  Grayish  green 

minations  Transparent  Dark  green 

M — Columnar,  fibrous,  to  opaque 

often  divergent; 

granular,  compact 


0 

HORNBLENDE 

Monoclinic 

Vitreous 

Blackish 

ft 

Silicate   of    Ca,    Mg, 
Fe,  Al,  etc. 

C  —  Long  prismatic, 
prism  angle  124°; 
often  with  rhombo- 
hedral-like  termi- 

Silky 
Translucent 
to  opaque 

green 
Dark  green 

nations 

312 

M—  Bladed,  fibrous, 
granular,  compact 

BRONZITE 

(Mg,Fe)2(Si03)2 

Orthorhombic 
C  —  Prismatic,  rare 
M  —  Fibrous,  lamellar, 
compact 

Bronzy 
Silky 
Translucent 
to  opaque 

Grayish  green 
Brownish 
green 
Olive  green 

YROXENES 

304 

DIOPSIDE 

CaMg(Si03)2 

Monoclinic 
C  —  Prismatic,  thick  col- 
umnar, prism  angle 

Vitreous 
Dull 
Transparent 

Pale  green 
Bright  green 
Dark  green 

87°  to 

M — Compact,    granular, 
columnar,  lamellar 


305 


(See  also  Augite  on  next  page). 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


477 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.          White                       C  —  Prismatic                   2.6      Crystals    may    appear    as 
6.                                         F  —  Conchoidal               2.8        though    fused.      Typical 
Brittle                                           contact  mineral.  In  meta- 

morphic  rocks,  especially 
granular  limestones. 
With  pyroxenes,  garnet, 
mica,  amphiboles,  wol- 
lastonite. 


White 
Greenish  white 


C — Prismatic,  often 
conspicuous, 
124° 
Brittle 


2.9      Often  as  radiating  masses. 

3.2  In  talc  and  chlorite 
schists.  With  serpentine, 
epidote,  calcite.  Nephrite 
and  jade  are  compact 
massive  varieties. 


6.          Gray  C — Prismatic,  often 

6.          Greenish  gray  conspicuous, 

Brownish  gray  124° 

Brittle 


2 . 9  Simple,  pseudohexagonal 
3.3  crystals,  and  cleavage — 
124° — important.  Com- 
mon in  many  types  of 
rocks.  With  quartz,  feld- 
spar, pyroxene,  chlorite, 
calcite. 


White 
Grayish 


C — Prismatic,  pina- 
coidal,  often 
conspicuous 

F — Uneven 

Brittle 


3.2      Cleavage     surfaces     often 
3 . 5        fibrous  or  lamellar,  irregu- 
lar   or    wavy,    with    dis- 
tinct   bronzy   luster. 
In  basic  igneous  rocks. 


White 
Gray 


C — Prismatic;  con- 
spicuous basal 
parting 

F — Uneven 

Brittle 


3 . 2  Crystals    prismatic    and 

3 . 3  pseudotetragonal   with 
distinct  basal  parting. 
May  have  colorless  and 
dark    green    zones.        In 
crystalline  limestones  and 
schists.     With   vesuvian- 
ite,  garnet,  scapolite, 
spinel,  apatite. 


478 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

AUGITE  Monoclinic  Vitreous  Blackish  green 

C — Short  prismatic,  thick  Submetallic      Leek  green 
Silicate   of    Ca,    Mg,  columnar,  prism          Translucent 

Fe,  Al,  etc.  angle  87°  to  opaque 

M — Compact,    granular, 
307  disseminated 


Willemite 


Turquois 

A12(OH)3PO4.H2O 
276 


Hexagonal  Vitreous  Apple  green 

C — Prismatic  Greasy  Yellowish 


Zn2SiO4 
289 

M  —  Compact,    granular, 
disseminated  grains 

Translucent 
to  opaque 

green 

OPAL 
SiO2.xH2O 

Amorphous 
M  —  Reniform,  botry- 
oidal,  compact 

Vitreous 
Greasy 
Translucent 

Green 
Bluish  green 
Blue 

232 

to  opaque 

Triclinic  Waxy  Sky  blue 

M — Reniform,    stalac-  Dull  Bluish 

titic,  disseminated  Opaque  to  green 

grains,  rounded  translucent  Apple  green 
pebbles 


Streak  —  Uncolored,  white,  or  light  gray 


MICROCLINE,  variety   Triclinic  Vitreous 

Amazonstone  C — Prismatic,  thick  tab-  Pearly 
KAlSiaOs                                ular,  twins  Translucent 
M — Cleavable,  granular,  to  trans- 
compact,  dissemi-  parent 
318                                        nated 


Bright  green 
Bluish  green 


LABRADORITE  Triclinic  Vitreous  Grayish  green 

C — Thin    tabular,    often  Pearly  Greenish 

Silicate  of  Ca,  Na,  Al          with  rhombic  cross-  Translucent 

section  to  nearly 

M — Compact,  cleavable,     opaque 
321  granular 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


470 


Hardness  3  to  6 


Hard-            Str 

ness 

Cleavage  =  C 
eak                  Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

5.          White 

C  —  Prismatic,   per- 

3.2 

Crystals  usually  eight- 

6.         Gray 

fect,    conspicu- 

3.6 

sided,   more  rarely  four- 

Greenish  gray              ous  —  87°,    (less 

sided  ;      pseudotetragonal 

distinct  than  on 

with  prism  angles  of  87° 

hornblende.) 

and    93°.    In  basic  rocks 

Brittle 

and  limestones. 

5.          White 

C—  Basal 

3.9 

Characterized   by   a  s  s  o- 

6. 

F  —  Uneven 

4.3 

ciates  —  f  ranklinite 

Brittle 

(black),  zincite  (red),  rho- 

donite (flesh  red),  calcite. 

6.6       White 

F  —  Conchoidal, 

2.1 

Structure      and      fracture 

6. 

conspicuous 

2.3 

characteristic.       Precious 

opal,  play  of  colors.     In 

veins,  cavities,  and  masses 

of  irregular  outline. 

6.          White 

F  —  Conchoidal 

2.6 

Secondary  mineral,  in  thin 

Greenish  white       Brittle 

2.8 

veins,  crusts,  or  coatings. 

With     quartz,    feldspar, 

kaolin,  limonite. 

Hardness  over  6 


6. 
6.6 


White 


C — Basal,  brachy- 
pinacoidal,  con- 
spicuous, 90° 
30' 

F — Uneven 

Brittle 


2 . 5  Slightly  inclined  cleavages ; 

2 . 6  may  show  twinning  stri- 
ations  on  basal  pinacoid. 
With  quartz,  other  feld- 
spars, mica,  hornblende, 
topaz. 


6 
6.6 


White 


C — Basal,  brachy- 
pinacoidal,  con- 
spicuous, 86° 

F — Uneven,  con- 
choidal 

Brittle 


2 . 7  Often  with  play  of  color — 
yellow,  green,  blue,  red. 
Inclined  cleavages  are 
striated.  In  basic  igne- 
ous rocks.  With  pyrox- 
enes, amphiboles. 


480 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

EPIDOTE 


Ca2(Al,Fe)2(A1.0H)(Si04): 


286 


Monoclinic                           Vitreous  Blackish  green 

C — Prismatic,    elongated  Transparent  Yellowish 

and  deeply  striated     to  opaque  green 

parallel    to    b    axis;  Brownish 

usually     terminated  green 

on  one  end  only  Pea  green 
M — Columnar,     fibrous, 
parallel    and    diver- 
gent; granular 


CYANITE  (Disthene,  kyan-  Triclinic 


Vitreous 


Al2SiO6 


ite)  C — Long  bladed,  without  Translucent 
good     terminations;    to  trans- 
sometimes       curved    parent 
and  radially  grouped 
M — Coarsely  bladed, 
columnar,  fibrous 


Sky  blue 
Greenish  blue 
Bluish  white 


282 


VESUVIANITE  Tetragonal  Vitreous  Green 

C — Short  prismatic  Greasy  Brownish 

i6[Al(OH,F)]Al2(SiO4)6     M — Compact,    granular,  Translucent  green 

aggregates  with  par-     to  opaque  Bluish 


Cae 


288 


aggregates  with  par- 
allel or  divergent 
striations 


OLIVINE  (Chrysolite,  Orthorhombic  Vitreous  Grass  green 

peridot)  C — Prismatic,  thick  tab-  Transparent  Olive  green 

(Mg,Fe)2SiO4  ular  to  trans-  Yellowish 

M — Rounded,      dissemi-  lucent  green 

nated  glassy  grains; 
289  granular  aggregates 


GARNET,  varieties 


R2'"R3" 

(SiO4)& 

R'"  =  Al,Fe,Cr 

R"  =  Ca,Fe,Mg 


ties  Cubic  Vitreous  Pale  green 

Grossularite  C — Dodecahedrons,     te-  Transparent  Grass  green 

Uvarovite  tragonal   trisoctahe-     to  opaque  Emerald 

Andradite  *i««««.     ^i— -    ~.   :« 


or   in 


drons,    alone 
combination 

M — Granular,  compact, 
lamellar,  dissemi- 
nated grains,  sand 


green 


290 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


481 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.          White                      C  —  Basal                         3.3      Crystals  are  often  dark  or 
7.          Grayish                  F  —  Uneven                      3.5       blackish    green,    massive 
Brittle                                           aggregates  lighter  colored. 

With  quartz,  feldspar, 
garnet,  hornblende,  py- 
roxene, magnetite,  native 
copper,  zeolites. 


6.          White                      C  —  Pinacoidal,  per- 
7.                                              feet,    conspicu- 
ous 
Brittle 

3.5      Color    irregularly    distrib- 
3.7       uted,    frequently   with 
lighter  longitudinal  mar- 
gins.      Hardness     varies 
with  direction,   4-5  par- 
allel to  long  direction,  6-7 
at  right  angles  thereto.    In 
gneiss,  mica  schist.    With 
staurolite,  corundum. 

6.6       White                     C—  Basal,  pris- 
matic, in- 
distinct 
F  —  Uneven 
Brittle 

3.3      In    crystalline    limestone, 
3  .  5        gneiss,  schists.    With  gar- 
net,   tourmaline,    chond- 
rodite,  wollastonite,   epi- 
dote,  pyroxene. 

6.6        White                      C  —  Pinacoidal 
7.          Yellowish  white     F  —  Conchoidal 
Brittle 

3.2      In    basic    rocks  —  basalts, 
3.6       traps;    crystalline,    lime- 
stones.      With      augite, 
magnetite,  spinel,  plagio- 
clase,  chromite,  pyrope. 

6.6        White 
7.6 


C — Dodecahedral, 
usually  in- 
distinct 

F — Conchoidal,  un- 
even 

Brittle 


3.4  Grossularite,  in  crystalline 
4.3  limestones  and  dolomites, 
with  wollastonite,  vesu- 
vianite,  diopside,  scapo- 
lite;  uvarovite,  in  ser- 
pentine, with  chromite, 
or  in  crystalline  lime- 
stones; andradite,  with 
feldspar,  nephelite,  leu- 
cite,  epidote,  magnetite. 


482 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

QUARTZ,  Phanerocrystal-  Hexagonal  Vitreous  Green 

line  varieties  C — Prismatic,      horizon-  Greasy  Greenish  blue 

SiO2  tally  striated  Transparent  Blue 

Cat's  eye  M — Compact,  granular        to  opaque  Blue  violet 
Amethyst 


222 


Cryptocrystalline    Hexagonal  Waxy  Light  green 

varieties  C — Never  in  crystals  Vitreous  Dark  green 

Chalcedony     M — Nodular,       spottedr  Translucent  Grayish  blue 

Chrysoprase  concretionary,    stal-     to  opaque  Greenish  blue 

actitic,  compact 

Heliotrope 


223 


TOURMALINE 

M9'Al3(B.OH)2Si4O19 
M'  =Na,K,Li,Mg,Fe 


284 


Hexagonal  Vitreous 

C — Prismatic,    vertically  Transparent 
striated;  terminated     to  trans- 
with  broken  or  rhom-    lucent 
bohedral-like  sur- 
faces 
M — Compact,  columnar 


Green 
Blue 


BERYL,  varieties  Hexagonal  Vitreous  Pale  green 

Emerald         C — Long  prismatic,  often  Transparent     Emerald  green 
Be3Al2(SiO3)6  Aquamarine  vertically  striated,     to  trans-          Bluish  green 

Common  large  lucent  Sky  blue 

M — Columnar,  granular, 
compact,  rounded 
pebbles 


313 


3.  GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


483 


7.          White 


Hardness  over  6 


1 

Hard-  !           Streak 
ness 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

i 

C — Indistinct  2.6      Characteristic     conchoidal 

F — Conchoidal,  fracture  and  glassy  luster. 

conspicuous  Chloritic  quartz,  green 

Brittle  from    included    chlorite; 

cat? s  eye,  opalescent,  due 
to  included  fibers  of  as- 
bestos ;  amethyst,  purple 
or  blue  violet,  usually  in 
crystals. 


7. 


White 


C — Indistinct  2.6      Not  as  glassy  as  phanero- 

F — Conchoidal,  crystalline  varieties. 

conspicuous  Chalcedony,     chrysoprase, 

Brittle  to  tough  prase,  plasma,  uniform  in 

color;  heliotrope,  spotted. 
To  distinguish,  see  refer- 
ence. 


7. 
7.6 


White 


C — None 

F — Conchoidal,  un- 
even 
Brittle 


2.9  Spherical  triangular  cross- 
3.2  section.  With  zonal  dis- 
tribution of  color — green, 
red,  colorless.  In  igneous 
and  metamorphic  rocks. 
With  lepidolite,  feldspar, 
quartz,  biotite. 


7.6 
8. 


White 


C — Indistinct 
F — Conchoidal,  un- 
even 
Brittle 


2.6  Crystals  usually  simple — 
2 . 8  prism  and  base.  Emerald, 
transparent  and  emerald 
green;  aquamarine,  trans- 
parent, bluish  to  sea  green 
or  yellowish  green.  In 
granitic  rocks,  mica 
schists,  clay  slates, 
placers.  With  quartz, 
feldspar,  mica,  topaz, 
tourmaline,  cassiterite, 
chrysoberyl,  garnet. 


484 


B.     MINERALS  WITH  NON-METALLIC  LUSTER 


Streak— Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

SPINEL,  varieties  Cubic  Vitreous  Grass  green 

C — Octahedral,     usually  Dull  Dark  green 

R"(R'"O2)2    Pleonaste  well  developed  Translucent  Grayish  green 

R"  =  Mg,Fe  Gahnite  M — Compact,    granular,  to  opaque  Light  blue 

Zn,  Mn  Blue  spinel  disseminated  grains 

R'"  =  Al,Fe 


267 


Chrysoberyl,  varieties 

Ordinary 

Be-  Alexandrite 

(A10,),  Cat's  eye 


Orthorhombic  Vitreous  Light  green 

C — Tabular;  heart-snap-  Greasy  Yellowish 

ed,  pseudohexagonal  Transparent  green 

twins  to  trans-  Emerald 

M — Compact;  loose,  lucent  green 

rounded  grains 


271 


CORUNDUM,  varieties 
Sapphire 


Al,0i 


Oriental  emerald 
Oriental  amethyst 
Common 


Hexagonal  Vitreous 

C — Prismatic,      tabular,   Transparent 
pyramidal,  rhombo-     to  opaque 
hedral;      rough     or 
rounded  barrel- 
shaped 

M — Compact,    granular, 
lamellar 


Green 
Blue 
Blue  violet 


228 


3.     GREEN,  BLUE,  OR  BLUE  VIOLET  IN  COLOR 


485 


7.6        White 
8.          Grayish 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Octahedral,  in- 
distinct 
F — Conchoidal 
Brittle 


3 . 5  Commonly  as  contact  min- 
4.4  eral  hi  granular  lime- 
stones; in  more  basic 
igneous  rocks ;  rounded 
grams  in  placers.  With 
calcite,  chondrodite,  ser- 
pentine, corundum, 
graphite,  pyroxenes. 


8.6        White 


C — Brachypina- 

coidal 
F — Uneven,  con- 

choidal 
Brittle 


3.6  Crystals  disseminated  as 
3.8  plates  with  feather-like 
or  radial  strfations.  Alex- 
andrite, red  in  trans- 
mitted light;  cat's  eye, 
opalescent.  In  mica 
schist,  gneiss;  granite;  also 
in  placers.  With  beryl, 
garnet,  tourmaline,  silli- 
manite. 


9.          White 


C — N  one;  nearly 
rectangular 
basal  and  rhom- 
bohedral  part- 
ings, conspicu- 
ous; often  stri- 
ated 

F — Conchoidal 
Brittle  to  tough 


3.9  When  massive,  often  mul- 
4 . 1  ti-colored — red,  gray,  yel- 
low. Sapphire,  trans- 
parent, blue ;  oriental 
emerald,  green,  transpar- 
ent ;  oriental  amethyst, 
violet.  In  limestone, 
granite,  syenite,  schist, 
peridotite;  placers.  With 
magnetite,  nephelite, 
mica,  chlorite,  spinel. 


486 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Carnotite 


K2O.2U2O3y2O6.3H2O? 


Orthorhombic                      Resinous  Canary 

C — Tabular,  small  rhom-  Vitreous  yellow 

bic  plates                      Dull  Greenish 

M — Scaly  aggregates,  in-    Transparent  yellow 

crustations,   crystal-     to  trans- 


277 

line  powder 

lucent 

BAUXITE 
A120(OH)4 

Never  in  crystals 
M  —  Pisolitic,  oolitic, 
round  disseminated 
grains,  clay-like, 
earthy 

Dull 
Earthy 
Opaque 

Yellow 
Yellowish 
brown 
Brown 

235 


LIMONITE,  varieties              M  —  Earthy,  porous, 

Earthy 

Yellow 

Yellow  ocher 

clay-like,  oolitic, 

Dull 

Yellowish 

Fe203.H2O 

Brown  ocher 

pisolitic 

Opaque 

brown 

- 

Bog  iron  ore 

Dark  brown 

Brown  clay 

• 

ironstone 

235 


ORPIMENT 

Monoclinic 

Greasy 

Lemon  yellow 

C—  Rare 

Pearly 

As2S3 

M  —  Foliated,     granular, 

Translucent 

reniform,        fibrous, 

204 

crusts 

REALGAR 

Monoclinic 

Resinous 

Reddish 

C  —  Short  prismatic,  rare 

Transparent 

yellow 

AsS 

M  —  Compact,    granular, 

to  trans- 

Orange yellow 

incrustations 

lucent 

203 


SULPHUR 


193 


Orthorhombic  Greasy 

C — Pyramidal,  tabular      Adamantine 
M — Granular,       fibrous,  Translucent 
earthy,  crusts,  com- 
pact 


Straw  yellow 
Honey  yellow 
Brownish 

yellow 
Reddish 

yellow 


4.  YELLOW  OR  BROWN  IN  COLOR 


487 


Hardness  1  to  3 


w     .                                           Cleavage  =  C        ~ 
Streak                   Fracture   =  F 
Tenacity                  Gr* 

cific          Characteristics  and 
vity                 Associates 

1.          Yellow                     C  —  Basal,  perfect 
2.                                           F—  Earthy 
Brittle 

Occurs  as  a  powder  or  in 
loosely  cohering  masses, 
intimately  mixed  with 
sand  and  sandstones. 
With  malachite,  azurite, 
biotite,  magnetite. 

1.          Yellow                    F  —  Earthy                      2.5      Color  and  streak  variable, 
3.          Brown                     Brittle                              2.6        due    to    pigments.     Clay 

1.          Yellow                    F—  Earthy 
3.          Brown                     Brittle 

2.5      Color  and  streak  variable, 
2.6        due    to    pigments.     Clay 
odor,  when  breathed 
upon.     Commonly     with 
pisolitic  or  oolitic  struc- 
ture.    With  clay  or  kaol- 
inite,  in  nodules,  grains, 
or    irregular    masses    in 
limestone  or  dolomite. 

1.          Yellowish  brown   F—  Earthy 
3.         Dark  brown 

3  .  4      Yellow  ocher,  earthy,   and 
4  .          yellow,   when  impure 
gritty  ;  brown  ocher,  earthy 
and  brown;  bog  iron  ore, 
porous;  brown  clay  iron- 
stone,    massive    or    con- 
cretionary,   impure   from 
clay,   sand.      Ocherous 
varieties  may  soil  fingers. 

1.6       Lemon  yellow         C  —  Clinopinacoidal, 
2.                                              usually  conspic- 
uous 
Slightly  sectile, 
laminse  flexible 

3.4      Characteristic   lemon   yel- 
3.5       low     color.       Frequently 
disseminated   in   clay  or 
dolomite.     With   realgar, 
stibnite,  barite,  calcite. 

1.6        Orange  yellow        C  —  Clinopinacoidal, 
2.                                              basal,  not  con- 
spicuous 
F  —  Conchoidal 
Slightly  sectile 

3.4      Redder  in  color  than  orpi- 
3.6        ment.     Disseminated     in 
clay  or  dolomite.     With 
orpiment,  stibnite,  native 
arsenic,  pyrite,  barite,  cal- 
cite. 

1.6        Pale  yellow             C  —  Indistinct 
2.6                                      C  —  Conchoidal 
Brittle 

1.9      Independent  beds  in  gyp- 
2.1        sum,  limestone;  in  lava, 
result  of  volcanic  exhala- 
tions.    With  celestite,  an- 
hydrite,  aragonite,    clay, 
metallic  sulphides. 

488 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Wulfenite 
PbMoO4 
259 

Tetragonal                           Greasy 
C  —  Square,  thin  tabular;  Adamantine 
more  rarely  pyrami-  Transparent 
dal                                   to  trans- 
M  —  Coarse,  fine  grained      lucent 

Wax  yellow 
Orange  yellow 
Brown 

Vanadinite 
FbsCKVOO, 
275 

Hexagonal                            Greasy 
C  —  Prismatic,    small,    at  Translucent 
times  skeletal                 to  opaque 
M  —  Compact,    globular, 
fibrous,  crusts 

Straw  yellow 
Brownish 
yellow 
Reddish 
brown 

Streak — Red,  brown,  or  yellow 


LIMONITE,  varieties 
Compact 
Fe2O3.H2O      Bog  iron  ore 
Brown  day 
ironstone 

236 

C  —  Always  pseudo-             Metallic 
morphs,  commonly     Dull 
after  pyrite,  marca-    Opaque 
site,  siderite 
M  —  Compact,  stalactitic, 
botryoidal,  nodular; 
often  with  internal, 
radial  fibrous  struc- 
ture; porous,  pisoli- 
tic,  oolitic 

Yellowish 
brown 
Dark  brown 

SIDERITE 
FeCO8 

248 

Hexagonal                           Vitreous 
C  —  Rhombohedral,             Pearly 
curved  or  saddle-        Dull 
shaped                          Translucent 
M  —  Cleavable,  granular,     to  nearly 
compact,  botryoidal,     opaque 
rarely  fibrous 

Light  brown 
Reddish 
brown 
Dark  brown 

SPHALERITE 

ZnS 

Cubic                                   Greasy 
C  —  Tetrahedral,  common  Submetallic 
M  —  Cleavable,     fine    or  Transparent 
coarse  grained,  com-     to  opaque 
pact 

Honey  yellow 
Yellowish 
brown 
Reddish 
brown 

205 


4.  YELLOW  OR  BROWN  IN  COLOR 


489 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 

Associates 

3. 

Lemon  yellow 
Pale  yellow 

C  —  Indistinct 
F  —  Conchoidal,  un- 
even 

6.3 

7. 

Square  plates,  sometimes 
with  forms  of  the  third 
order.  With  lead  min- 

Brittle 

erals  —  galena,  pyromor- 
phite,  vanadinite. 

3. 

Pale  yellow 
Yellow 

C—  None                        6.7 
F  —  Conchoidal,  un-       7  .  2 
even 

Crystal  faces  smooth  with 
sharp  edges.  With  lead 
minerals,  but  never  in 

Brittle 

large  quantities. 

Hardness  over  3 


3.          Yellowish  brown   F — Conchoidal, 
6.6  splintery, 

earthy 
Brittle 


3.4  Often  with  black  varnish- 
4.  like  surface  and  passing 
into  soft,  yellow  ocherous 
variety.  Compact  limon- 
ite,  massive  with  fibrous 
structure,  rather  pure; 
bog  iron  ore,  porous ;  brown 
day  ironstone,  massive  or 
concretionary,  impure 
from  clay,  sand. 


3.6 

4. 


Pale  yellow 
Yellowish  brown 


C — Rhombohedral, 

conspicuous 
F — Conchoidal 
Brittle 


3 . 7  Curved  crystals  and  rhom- 
3.9  bohedral  cleavage  char- 
acteristic. In  ore 
deposits;  beds  and  con- 
cretions in  limestones  and 
shales.  With  pyrite,  chal- 
copyrite,  galena,  tetra- 
hedrite,  cryolite. 


3.6 
4. 


Pale  yellow 
Light  brown 


C— Dodecahedral, 
usually  conspic- 
uous 

F — Conchoidal 

Brittle 


3.9  Distinguished  from  sider- 
4.2  i  t  e  b  y  crystallization, 
more  greasy  luster,  and 
cleavage.  Color  and 
streak  vary  with  im- 
purities. Extensively  in 
limestones.  With  galena, 
chalcopyrite,  pyrite,  rho- 
dochrosite,  barite,  fluor- 
ite. 


490 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

PYROMORPHITE 

Pb5Cl(P04)3 

275 


Hexagonal 

C — Prismatic,  thick 

tabular,  rounded 

and  barrel-shaped; 

acicular 
M — Globular,    reniform, 

disseminated,  crusts 


Greasy  Wax  yellow 

Adamantine  Green  yellow 

Translucent  Yellowish 
to  opaque         brown 


Zincite 
ZnO 


Hexagonal  Adamantine  Orange  yellow 

C — Small,  rare  Vitreous  Reddish 

M — Compact,  granular,  Translucent  yellow 
foliated                           to  opaque 


228 

Huebnerite 
MnWO4 

260 

Monoclinic                            Greasy 
C  —  Long  fibrous,  bladed,  Submetallic 
stalky;  often  diver-  Translucent 
gent,    without   good     to  opaque 
terminations 
M  —  Compact,     lamellar, 
granular 

Reddish 
brown 
Hair  brown 
Pale  yellow 

WOLFRAMITE 
(Fe,Mn)W04 

261 

Monoclinic                           Submetallic 
C  —  Thick  tabular,  short  Opaque 
columnar,  often 
large 
M  —  Bladed,  curved  lam- 
ellar, granular,  com- 
pact 

Reddish 
brown 
Dark  brown 

Ferberite 
FeWO4 

261 

Monoclinic                           Submetallic 
C  —  Wedge  shaped,  short  Opaque 
prismatic,  tabular 
M  —  Fan    shaped    aggre- 
gates, bladed,  granu- 
lar, compact 

Brown 
Blackish 
brown 

RUTILE 

TiO2  or  TiTiO4 

224 

Tetragonal                           Adamantine 
C  —  Prismatic,    vertically  Submetallic 
striated  ;       twinned  Translucent 
yielding  knee-shaped     to  opaque 
or  rosette  forms 
M  —  Compact,      dissemi- 
nated 

Reddish 
brown 
Yellowish 
brown 
Dark  brown 

4.  YELLOW  OR  BROWN  IN  COLOR 


491 


Hardness  over  3 

Hard-             gt 

ness 

Cleavage  =  C 

reak                  Fracture  =  F 
Gra 
Tenacity 

cine          Characteristics  and 
vity                  Associates 

3.5        Yellow                     C  —  None                         6.5      Common  alteration  prod- 

4.          Greenish  yellow     F  —  Conchoidal,  un-        7  .  1        uct  of  lead  minerals. 

even 

With     galena,     cerussite, 

Brittle 

barite,   limonite. 

4.          Orange  yellow        C  —  Basal,  some-             5.4      Recognized    by  associates. 
4.6        Reddish  yellow             times  conspicu-        5.7        With   calcite,    franklinite 
ous                                            (black),  willemite  (yellow 

F  —  Uneven 

to  green),  rhodonite  (flesh 

Brittle 

red).     On    exposure    be- 

comes   coated    with    the 

white  carbonate. 

4.5        Yellowish  brown    C  —  Clinopinacoidal, 

6.7      Structure,    cleavage,    and 

5.6 

conspicuous 

7  .  3        high  specific  gravity  char- 

Brittle 

acteristic.     In  quartz 

veins.     With  wolframite, 

fluorite,  pyrite,  scheelite. 

galena,  tetrahedrite. 

6.          Reddish  brown      C  —  Clinopinacoidal, 

7.1      Distinguished  from  hueb- 

6.5       Dark 

brown                  conspicuous 

7.5        nerite   by   streak.     Pow- 

F —  Uneven 

der  may  be  slightly  mag- 

Brittle 

netic.     With     cassiterite, 

quartz,      mica,      apatite, 

scheelite,       molybdenite, 

huebnerite. 

5.          Brown                    C  —  Clinopinacoidal, 

7.5      In  granites  and  pegmatites. 

6.6       Dark 

brown                  perfect 

With    quartz,    chalcopy- 

F  —  Uneven 

rite,  galena,  scheelite. 

Brittle 

6.          Pale  yellow             C  —  Prismatic,    py- 
7.          Pale  brown                   ramidal,  not 

4  .  2      Not  as  heavy  as  cassiterite. 
4.3        Often  in  fine  hair-like  in- 

conspicuous 
F — Uneven 
Brittle 


elusions.  With  quartz, 
feldspar,  hematite,  ilmen- 
ite,  chlorite,  brookite. 


492 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Red,  brown,  or  yellow 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CASSITERITE 

SnO2  or  SnSnO4 


226 


Tetragonal 

C — Thick  prismatic;  Greasy 

knee-shaped  twins       Dull 

quite  common  Translucent 

M — Compact,    reniform,     to  opaque 

botryoidal,   rounded 

pebbles,   often  with 

internal,  radial 

fibrous  structure, — 

wood  tin 


Adamantine     Reddish 
Yellowish 
brown 
Dark  brown 


SPINEL,  variety 
Picotite 
(Mg,Fe)2(Al,Cr)204 

268 


Cubic  Vitreous 

C— Octahedral,  small         Dull 
M — Compact,    granular,   Nearly 
disseminated  grains      opaque 


Yellowish 
brown 

Greenish 
brown 

Brown 


Streak — Uncolored,  white  or  light  gray 


Cerargyrite  (Horn  silver) 
AgCl 


Cubic  Waxy 

C — Rare  Greasy 

M — Wax-like  crusts  and  Transparent 
coatings;  stalactitic,     to  trans- 
dendritic  lucent 


Yellowish 
Brownish 


238 


TRIPOLITE  (Opal) 
SiO2.xH2O 

Amorphous 
M  —  Porous,  earthy, 
chalk-like 

Vitreous 
Dull 
Translucent 
to  opaque 

Yellow 
Yellowish 
brown 
Brown 

234 

j 

KAOLINITE  (Kaolin) 

Monoclinic 
C  —  Scaly,    hexagonal 

Dull 
or  Pearly 

Yellowish 
Brownish 

H4Al2Si2O9 


orthorhombic      out-  Earthy 
line,  rare  Opaque  to 

M — Compact,       friable,     translucent 
mealy,  clay-like 


301 


4.  YELLOW  OR  BROWN  IN  COLOR 


493 


Hardness  over  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.         Pale  brown            C  —  Indistinct                 6  .  8      Recognized  by  high  specific 
7.         Pale  yellow            F  —  Uneven                     7  .  2       gravity.     In  veins  cutting 
Brittle                                         granite,  gneiss;  in  alluvial 

deposits  as  stream  tin. 
With  quartz,  mica,  wol- 
f  r  a  m  i  t  e,  arsenopyrite, 
molybdenite,  tourmaline, 
fluorite,  chlorite. 


7.5       Pale  brown  C — Indistinct  4 . 1      Commonly  in  basic  igneous 

8.  F — Conchoidal  rocks,   especially  olivine- 

Brittle  bearing  types.     With  ser- 

pentine,   olivine,    corun- 
dum, magnetite,  garnet. 


Hardness  1  to  3 


1.         White,  shiny          C — None  5.5      Cuts    like    wax,    yielding 

1.5       Gray,  shiny  F — Conchoidal  5.6       shiny    surfaces;    on    ex- 

Highly  sectile  posure    turns   violet, 

brown,  or  black.  With 
silver  minerals,  especially 
argentite,  native  silver; 
also  limonite.  calcite, 
barite. 


1. 
2.5 


White 
Gray 


F— Earthy 
Friable 


2.1  Apparently  very  soft,  but 
2 . 3  fine  particles  scratch 
glass.  Resembles  kaolin- 
ite,  but  gritty  and  not 
plastic .  Due  to  impurities 
may  have  clay  odor. 


1. 
2.5 


White 
Yellowish  white 


C — Basal, — scales 
F— Earthy 
Brittle 


2.2      Not   gritty   like    tripolite. 

2.6  Very  strong  clay  odor 
when  breathed  upon. 
Usually  adheres  to  tongue 
and  becomes  plastic  when 
moistened.  Greasy  feel. 
With  quartz,  feldspar,  cor- 
undum, topaz. 


494 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

TALC,  variety  Monoclinic  Greasy  Yellowish 

Soapstone  or  steatite   M — Compact,    globular,   Pearly  Yellowish 

H2MgsSi4Oi2  granular  Translucent  brown 

to  opaque  Brownish 


299 


Asbestos,  variety 
Chrysotile 
H4Mg3Si2O9 


Orthorhombic  ?  Silky  Yellowish 

M — Fibrous,    coarse    or  Greasy  Brownish 

fine ;  felted  Opaque 


298 


variety  Monoclinic                           Silky                  Yellowish 

Amphibole  M — Fibrous,    coarse    or  Dull                   Brownish 

Silicate  of  Ca,  Mg,  Fe,  Al,  fine ;  felted ;  compact,  Opaque 

etc.  leather-  or  cork-like 


311 


SODA  NITER   (Chile  salt-  Hexagonal 

peter)  C — Rare 

NaNO3  M — Granular,  crusts, 
241  efflorescences 


Vitreous  Yellowish 

Transparent     Lemon  yellow 
Reddish 
brown 


GYPSUM,  varieties  Monoclinic 

Selenite        C — Tabular,  prismatic; 
H2O      Satin  spar          swallow  tail  twins 
Ordinary     M — Cleavable,  coarse 
and  fine  grained, 
fibrous  foliated, 
earthy 


Pearly 
Vitreous 
Silky 
Dull 

Transparent 
to  opaque 


Yellow 

Honey  yellow 
Brown 


264 
SULPHUR 


193 


Orthorhombic 

C  —  Pyramidal,  tabular       Greasy 

M  —  Compact,  granular,     Translucent 

fibrous,  earthy, 

crusts 


Adamantine     Straw  yellow 
Brownish 

yellow 
Reddish 

yellow 


4.  YELLOW  OR  BROWN  IN  COLOR 


495 


Hardness  1  to  3 


Cleavage  =  C 
Hard"             Streak                  Fracture  =  F         ^pec 
Tenacity 

ific         Characteristics  and 
rity                 Associates 

1.          White                      F  —  Uneven,                     2.6      Greasy  or  soapy  feel  im- 
2.5        Yellowish  white           splintery                   2.8        portant.       Soapstone     or 
Sectile                                           steatite,     coarse     to     fine, 
granular,  more  or  less  im- 
pure.    Hardness     varies. 
With  serpentine,  chlorite, 
dolomite,    magnesite, 
actinolite. 

1.          White                      F  —  Fibrous                      1  .         Delicate,  fine,  parallel,  flex- 
3.                                          Flexible                            2.5        ible   fibers,  perpendicular 
to  walk,  easily  separable 
—  short    fibered     asbestos, 
compare  below.     In  veins 
or  seams  in  serpentine. 

1.          White                      F  —  Fibrous                      1.        Long  fibered  asbestos,  par- 
3.                                        Flexible,  tough               2.5       allel,  flexible  fibers,  par- 
allel to  walls.     Compare 
above.     Mountain  leather, 
mountain  cork,   mountain 
wood,  compact  but  light 
and  tough. 

1.6        White                      C  —  Rhombohedral         2.1      Cooling  and  saline  taste. 
2.                                         F  —  Conchoidal               2  .  3        Absorbs  moisture  readily. 
Brittle                                           In  deposits  with  gypsum, 
sand,  clay,  guano. 

1.5        White                      C  —  Clinopinacoidal,       2  .  2      Selenite,  crystals  and  cleav- 
2.                                                conspicuous;             2.4        able  plates,  usually  trans- 

1.5 
2.5 


pyramidal, 
orthopinacoidal 
F — Conchoidal, 

fibrous 

Brittle,  laminae 
flexible 


White  C— Indistinct 

Yellowish  white     F — Conchoidal 
Brittle 


1.9 
2.1 


parent ;  satin  spar,  fibrous 
with  silky  luster;  ordinary, 
granular.  In  limestones 
and  shales.  With  halite, 
celestite,  sulphur,  arago- 
nite,  anhydrite;  ore 
deposits. 

Independent  beds  in  gyp- 
sum, limestone;  in  lava, 
result  of  volcanic  exhala- 
tions. With  celestite,  an- 
hydrite, aragonite,  clay, 
metallic  sulphides. 


496 


B.    MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

HALITE  (Rock  salt) 
NaCl 

236 


Cubic  Vitreous  Yellow 

C — Cubes,  often  skeletal  Transparent  Yellowish 

or  hopper-shaped  to  trans-  brown 

M — Compact,  cleavable,  lucent  Brownish 

granular,  fibrous, 

stalactitic,  crusts 


MUSCOVITE 

(Isinglass) 
H2KAl3(SiO4)3 


Monoclinic  Vitreous  Light  yellow 

C — Tabular,    pyramidal,  Pearly  Yellowish 

with     orthorhombic  Transparent       brown 
or  hexagonal  outline;    to  trans-         Light  brown 
often  large  and  rough    lucent 
M — Scales,    plates ;   foli- 
ated   and    plumose 
aggregates 


295 


PHLOGOPITE 


(K,H)3Mg3Al(Si04)3 


Monoclinic  Pearly  Yellow 

C — Prismatic,      tabular,  Submetallic      Yellowish 

with    hexagonal    or  Transparent       brown 

orthorhombic      out-     to  trans-          Brown 

line;  often  large  and     lucent 

coarse 
M — Plates,  disseminated 


294 


APATITE,  variety  Hexagonal  Dull 

Phosphate  rock  M — Compact,  fibrous,        Opaque 
Ca5F(PO4)3,  chiefly  nodular,  reniform, 

earthy 
273 


Brown 


4.    YELLOW  OR  BROWN  IN  COLOR 


497 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

2.         White                     C—  Cubic, 

perfect,        2  .  1      Pigment  usually  iron  oxide. 

2.6                                              conspic 

uous              2.3        May  absorb  moisture  and 

F — Conchoidal 
Brittle  - 


become  damp.  Charac- 
teristic cubical  cleavage 
and  saline  taste.  With 
shale,  gypsum,  anhydrite. 


White 


C— Basal,    perfect,        2.8 
conspicuous  3 . 1 

Tough  laminae  very 
elastic 


Lighter  colored  than  phlo- 
gopite.  Structure,  perfect 
cleavage,  and  elasticity 
important.  Crystals  may 
show  distinct  partings 
perpendicular  to  cleav- 
age— ruled  mica.  In 
granitic  rocks,  schists, 
limestones.  With  feld- 
spar, quartz,  tourmaline, 
beryl,  garnet. 


2.          White 
3. 


C — Basal,    perfect, 
conspicuous 

Tough,  laminae 
very  elastic 


2.8  Usually  amber  brown  or 
3 . 1  bronze  in  color.  When 
cleavage  laminae  are  held 
close  to  the  eye  in  view- 
ing a  source  of  light  a 
star-like  form  is  some- 
times observed.  Especi- 
ally characteristic  pf 
c  ry  s  t  a  Hi  n  e  limestones, 
dolomites,  schists.  With 
pyroxenes,  amphiboles, 
serpentine. 


White 


F — Conchoidal,  3 . 1      More   or   less   impure 

uneven  3.2       masses,     frequently     re- 

Brittle  sembling    compact   lime- 

stone.   Independent  beds, 
nodules,  concretions. 


498 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster                -~  , 
„                                Color 
Transparency 

BARITE  (Heavy  spar) 
BaSO, 

256 

Orthorhombic 
C  —  Tabular,      prismatic, 
very  common;  crest- 
ed divergent  groups 
M  —  Compact,     lamellar, 
fibrous,  cleavable, 
reniform 

Vitreous            Yellowish 
Pearly                Brownish 
Transparent     Dark  brown 
to  opaque 

CALCITE,  varieties                  Hexagonal                            Vitreous            Honey  yellow 
Dog  tooth  spar     C  —  Scalenohedral,  rhom-  Dull                   Yellowish 
CaCOs        Nail  head  spar           bohedral;  prismatic;  Transparent       brown 
Limestone                    tabular,        acicular;     to  nearly         Dark  brown 
Marble                        may  be  highly  modi-     opaque 
fied  and  twinned 
Calcareous  tufa  M  —  Cleavable,  granular, 
Travertine                    fibrous,  banded,  stal- 
Stalactites,  etc.             actitic,   oolitic,   por- 
ous, compact,  crusts, 
242                                              shells 

Wulfenite 
PbMoO4 
259 

Tetragonal                            Greasy               Wax  yellow 
C  —  Square,     thin    tabu-  Adamantine     Orange  yellow 
lar;  more  rarely  py-  Transparent     Brown 
ramidal                           to  trans- 
M  —  Coarse,  fine  grained      lucent 

Vanadinite 
Pb5Cl(V04)3 
.     275 

Hexagonal                            Greasy               Straw  yellow 
C  —  Prismatic,    small,    at  Translucent      Brownish 
times  skeletal                to  opaque         yellow 
M  —  Compact,    globular,                             Reddish 
fibrous,  crusts                                         brown 

Streak  —  Uncolored,  white,  or  light  gray 

BARITE  (Heavy  spar) 
BaSO4 

Orthorhombic                      Vitreous            Yellowish 
C  —  Tabular,      prismatic,   Pearly               Brownish 
very  common;  crest-  Transparent     Dark  brown 

ed     and     divergent 
groups 

M — Compact,    lamellar, 
fibrous,  cleavable, 
reniform 


to  opaque 


256 


4.  YELLOW  OR  BROWN  IN  COLOR 


499 


Hardness  1  to  3 


Cleavage  =  C 
Streak                  Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

i 

1 

2.5        White                      C  —  Basal,    p  r  i 

s-        4.3 

Characterized    by    rather 

3.                                                matic,     usually        4.7 

high  specific  gravity  and 

conspicuous 

cleavages.     In  metallifer- 

F —  Uneven 

ous  veins;  pockets,  lentic- 

Brittle 

ular  masses  in  limestones. 

With   galena,    sphalerite, 

fl  u  o  r  i  t  e,  chalcopyrite; 

manganese  and  iron  min- 

erals. 

3.          White 


C — Rhombohedral, 
usually  conspic- 
uous 

F — Conchoidal 

Brittle 


2.7  Often  in  extensive  de- 
posits. Rhombohedral 
cleavage  characteristic 
especially  on  crystals. 
Cleavage  surfaces  often 
striated.  Very  strong 
double  refraction  easily 
observed  when  transpar- 
ent. To  distinguish  var- 
ieties, see  reference. 


White  C — Pyramidal,  in- 

Yellowish  white  distinct 

F — Conchoidal,  un- 
even 

Brittle 


6.3      Square    plates    sometimes 
7.          with  forms  of  the  third 
order.     With    lead    min- 
erals— galena,     pyromor- 
phite,  vanadinite. 


White  C— None 

Yellowish  white     F — Conchoidal,  un- 
even 
Brittle 


6.7      Crystal  faces  smooth  with 
7.2        sharp  edges.     With  lead 

minerals,    but    never    in 

large  quantities. 


3. 
3.5 


White 


Hardness  3  to  6 


C — Basal,  p  r  i  s- 
matic,  usually 
conspicuous 

F — Uneven 

Brittle 


4.3  Characterized  by  rather 
4.7  high  specific  gravity  and 
cleavages.  In  metallifer- 
ous veins;  pockets,  lentic- 
ular masses  in  limestone. 
With  galena,  sphalerite, 
flu  o  rite,  chalcopyrite; 
manganese  and  iron  min- 
erals. 


500 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CERUSSITE 
PbCO3 

251 

Orthorhombic                      Adamantine 
C  —  Tabular,     prismatic,     Greasy 
pyramidal;    pseudo-  Silky 
hexagonal;     clusters  Transparent 
and  star-shaped             to  trans- 
groups                            lucent 
M  —  Interlaced    bundles, 
granular,  stalactitic, 
compact 

Yellow 
Yellowish 
brown 

STILBITE  (Zeolite) 
(Ca,Na2)Al2Si6016.6HO 

326 

Monoclinic                           Vitreous 
C  —  Twinned,    sheaf-like,   Pearly 
radial     or     globular  Transparent 
aggregates                      to  trans- 
lucent 

Yellowish 
Yellowish 
brown 
Brownish 

SERPENTINE 

H4Mg3Si2O9 

Orthorhombic  ?                  Greasy 
C  —  Unknown                       Waxy 
M  —  Compact,  columnar,  Translucent 
fibrous,  lamellar,           to  opaque 
granular 

Greenish 
brown 
Greenish 
yellow 
Yellowish 
brown 

297 


APATITE,  variety  Hexagonal  Dull 

Phosphate  rock  M  —  Compact,  fibrous,        Opaque 
Ca6F(PO4)3,  chiefly  nodular,  reniform 


Brown 


273 


Wavellite 

(A1.OH)3(PO<)2.5H2O 

276 


Orthorhombic 
C — Capillary,  small 
M — Crusts,  globular, 
hemispherical  aggre- 
gates, with  radial  fi- 
brous structure 


Vitreous 
Translucent 


Yellow 
Brown 


DOLOMITE 

CaMg(CO3)2 

245 


Hexagonal  Vitreous  Yellowish 

C — Rhombohedral,  with  Transparent       brown 

curved  surfaces  to  trans-  Grayish 

M — Coarsely  crystalline,  lucent  brown 

compact,     granular,  Dark  brown 

friable 


4.  YELLOW  OR  BROWN  IN  COLOR 


501 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3. 
3.5 

White                      C  —  Indistinct                  6  .  4      Twinning,   structure, 
Gray                        F  —  Conchoidal               6.6        luster,  and  specific  grav- 
Brittle                                           ity  characteristic.     With 

lead  minerals — g  ale  na, 
pyromorphite,  anglesite; 
also  malachite,  limonite. 


3.          White                      C—  Indistinct 
4.                                         F  —  Uneven 
Brittle 

2  .  1      Radial  and  sheaf-like  struc- 
2  .  2        ture  important.     In  basic 
igneous  rocks  and  ore  de- 
posits.    With   chabazite, 
apophyllite,     d  a  t  o  1  i  t  e, 
calcite. 

3.          White                      F—  Conchoidal, 
4.                                                splintery 
Brittle 

2.5      Smooth    and    greasy   feel. 
2.8       Often    spotted,    clouded, 
mult  i-colored.     Some- 
times crossed  by  seams  of 
asbestos  (chry  sotile). 
With     magnesite,     chro- 
mite,   garnierite,   pyrope, 
platinum,  calcite. 

3.          White                       F  —  Conchoidal,  un- 
6.                                                even 
Brittle 

3  .  1      More    or   less   impure 
3.2       masses,  frequently  re- 
sembling compact,  brown 
limestone.      Independent 
beds,  nodules,  c  o  n  c  r  e- 
tions. 

3.5        White                      C  —  Pinacoidal, 
4.                                                domatic 
F  —  Uneven,  fibrous 
Brittle 

2.3      Secondary  mineral  occur- 
2.4        ring  on  surfaces  of  rocks 
or  minerals,  as  crystalline 
crusts    with    pronounced 
radial  fibrous  structure. 

3.5 
4. 


White 
Gray 


C — Rhombohedral, 

perfect 

(crystals) 
F— Conchoidal 
Brittle 


2.9  Crystals  generally  curved 
or  saddle-shaped.  Marble 
includes  some  compact 
varieties.  Independent 
beds;  in  fissures  and  cav- 
ities; with  ore  deposits. 


502 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Crystallization 

Name,  Composition,  and 

Structure 

Luster 

Onlor 

Reference 

Crystals  =  C 

Transparency 

v^oior 

Massive  =  M 

ARAGONITE 

Orthorhombic 

Vitreous 

Wine  yellow 

C  —  Chisel-      or      spear- 

Resinous 

Yellowish 

CaCO3 

shaped  ;    pseudohex- 

Transparent 

brown 

agonal  prisms; 

to  trans- 

radial, columnar, 

lucent 

acicular  aggregates 

M  —  Stalactitic,  reniform, 

249 

crusts,  oolitic 

STRONTIANITE 

Orthorhombic 

Vitreous           Yellow 

C  —  Spear-shaped,  colum- 

Greasy             Yellowish 

SrC03 

nar,   acicular;  often 

Transparent 

brown 

in  divergent  groups 

to  trans- 

Brown 

M  —  Granular,    compact, 

lucent     • 

botryoidal,  fibrous 

250 

SIDERITE 

Hexagonal 

Vitreous 

Light  brown 

C  —  Rhombohedral, 

Pearly 

Reddish 

FeCO3 

curved  or  saddle- 

Dull 

brown 

shaped,  common 

Translucent 

Dark  brown 

M  —  Cleavable,  granular, 

to  nearly 

compact,  botryoidal, 

opaque 

rarely  fibrous 

248 


SPHALERITE 

ZnS 


Cubic  Resinous 

C — Tetrahedral,  common  Submetallic 
M — Cleavable,   fine  and  Translucent 

coarse  grained,  com-     to  opaque 

pact 


Honey  yellow 
Yellowish 

brown 
Reddish 

brown 


205 


PYROMORPHITE 

Pb6Cl(P04)3 

275 


Hexagonal  Greasy  Wax  yellow 

C — Prismatic,  thick  tab-  Adamantine  Greenish 

ular,    rounded    and  Translucent  yellow 

barrel-shaped;  acicu-     to  opaque  Yellowish 

lar  brown 
M — Globular,    reniform, 
disseminated,  crusts 


4.  YELLOW  OR  BROWN  IN  COLOR 


503 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.5        White                      O—  Pinacoidal,                2.9      Twins  common,  of  ten  pseu- 
4.          Gray                              prismatic                   3            dohexagonal  —  prism    and 

F — Conchoidal 
Brittle 


striated  base.  In  cracks 
and  cavities;  with  ore 
deposits;  deposition  from 
hot  springs;  in  shells. 
With  gypsum,  celestite, 
sulphur,  siderite,  zeolites. 


3.5 

4. 


White 
Gray 


C — Prismatic,  indis- 
tinct 

F — Uneven 
Brittle 


3.6  Structure  similar  to  ara- 
3.8  gonite.  Divergent  col- 
umnar masses  and  higher 
specific  gravity  character- 
istic. In  ore  deposits ;  in- 
dependent beds.  With 
galena,  barite,  calcite. 


3.5 

4. 


Gray 
White 


C — Rhombohedral, 

conspicuous 
F — Conchoidal 
Brittle 


3.7  Distinguished  from  sphal- 
3.9  erite  by  curved  crystals 
and  rhombohedral  cleav- 
age. In  ore  deposits ;  beds 
and  concretions  •in  lime- 
stones and  shales.  With 
p  y  r  i  t  e,  chalcopyrite, 
galena,  tetrahedrite,  cryo- 
lite. 


3.5 
4. 


White 
Yellowish  white 


C — Dodecahedral, 
usually  conspic- 
uous 

F — Conchoidal 

Brittle 


3.9  Resinous  luster  and  cleav- 
4 . 2  age  important.  Color  and 
streak  vary  with  im- 
purities. Extensively  in 
limestones.  With  galena, 
chalcopyrite,  pyrite,  bar- 
ite, fluorite,  rhodochro- 
site. 


3.5 

4. 


White 
Yellowish  white 


C — None 

F — Conchoidal,  un- 
even 
Brittle 


6.5      Common  alteration  prod- 
7 . 1        uct     of     lead     minerals. 

With     galena,     cerussite, 

barite,   limonite. 


504 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

FLUORITE  (Fluor  spar) 
CaF2 


Cubic  Vitreous  Wine  yellow 

C — Cubes,  alone  or  modi-  Transparent  Yellowish 

fied,  well  developed      to  nearly  brown 

M — Cleavable,  granular,     opaque  Brown 

fibrous 


239 


Scheelite 
CaW04 

269 


Tetragonal  Greasy  Pale  yellow 

C — Pyramidal,   small,  Adamantine  Yellowish 

more  rarely  tabular    Transparent  brown 

M — Drusy   crusts,    reni-     to  trans-  Grayish 

form,  granular,  com-     lucent  brown 

pact 


APATITE 

Ca6F(P04)3 


Hexagonal  Greasy  Brown 

C — Prismatic,  thick  tab-  Vitreous  Greenish 

ular,  sometimes  Translucent       brown 

large,  with  rounded  to  opaque       Reddish 
edges  brown 

M — Compact,       fibrous,  Yellow 

nodular,  reniform 


273 


HEMIMORPHITE     (Gala-  Orthorhombic  Vitreous  Yellow 

mine)   C — Thin  tabular,  pyram-  Dull  Yellowish 

H2Zn2SiO6  idal,  hemimorphic,  Transparent       brown 

highly  modified  to  trans-          Brown 
M — Compact,    globular,     lucent 

granular,  stalactitic, 
280  cellular,  earthy 


Huebnerite 
MnW04 

260 


Monoclinic  Resinous  Reddish 

C — Long  fibrous,  bladed,  Submetallic        brown 

stalky;  often  diver-  Translucent     Hair 

gent,    without  good  to  opaque         brown 
terminations  Pale  yellow 

M — Compact,     lamellar, 
granular 


4.  YELLOW  OR  BROWN  IN  COLOR 


505 


4. 


White 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Octahedral, 
perfect,  con- 
spicuous 

Brittle 


3 .        Recognized  by  crystal 
3 . 2       form,  octahedral  cleavage, 
and  hardness.     Common 
gangue   of  metallic   ores, 
especially   galena,    sphal- 
erite, cassiterite ;  also  with 
.    calcite,  barite. 


4.5       White 


C — Pyramidal,  not 
conspicuous 

F — Conchoidal,  un- 
even 

Brittle 


5 . 9  Small,  well  developed  octa- 
6.2  hedral-like  crystals,  usu- 
ally on  guartz;  when 
massive  high  specific  grav- 
ity important.  With  cas- 
siterite, wolframite,  fluor- 
ite,  apatite,  molybdenite. 


4.5 
5, 


White 


C — Basal,  imperfect 
F — Conchoidal,  un- 
even 
Brittle 


3 . 1  Crystals  may  be  vertically 

3.2  striated  and  have  fused 
appearance.      Color    un- 
evenly distributed,  often 
with  greenish  spots.     In 
crystalline        limestones; 
metalliferous  deposits;  ig- 
neous  rocks.     With 
quartz,    cassiterite,  fluor- 
ite,  wolframite. 


4.5        White  C — Prismatic 

5.  F — Uneven,   c  o  n- 

choidal 
Brittle 


3 . 3  Crystals  often  in  sheaf -like 
3.5  groups  or  druses  in  cav- 
ities. When  ma  s  s  i  v  e, 
often  porous  or  cellular. 
In  limestones.  With 
sphalerite,  galena,  and 
especially  smithsonite. 


4.5 
5.5 


Greenish  gray 


C — Clinopinacoidal,       6 . 7 
conspicuous  7 . 3 

Brittle 


Structure,  cleavage,  and 
specific  gravity  charac- 
teristic. In  quartz  veins. 
With  wolframite,  fluorite, 
pyrite,  scheelite,  galena, 
tetrahedrite. 


506 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Crystallization 

Name,  Composition,  and 

Structure 

Luster 

Cnlnr 

Reference 

Crystals  =  C 

Transparency 

VyUlUi 

Massive  =  M 

SMITHSONITE 

Hexagonal 

Vitreous 

Brown 

C  —  Small,  usually  as 

Dull 

Yellowish 

ZnCO3 

druses  or  crusts 

Translucent 

brown 

M  —  Botryoidal,  stalactit-     to  nearly 

Orange 

ic,  fibrous,  compact 

,     opaque 

yellow 

cellular,  granular 

" 

247 

Natrolite  (Zeolite) 

Orthorhombic 

Vitreous 

Yellowish 

C  —  Slender  prismatic, 

Silky 

Na2Al(AlO)(SiO3)3.2H2O 

nearly  square,  radial   Transparent 

or  interlacing  groups     to  trans- 

M  —  Fibrous,  granular, 

lucent 

324 

compact 

TITANITE  (Sphene) 

Monoclinic 

Vitreous 

Brown 

C  —  Wedge-  or  envelope-  Greasy 

Reddish 

CaTiSi05 

shaped     when     dis-  Transparent 

brown 

seminated;     tabular     to  opaque 

Yellow 

or    prismatic    when 

attached 

323 

M  —  Compact,  lamellar 

Monazite 

Monoclinic 

Greasy 

Reddish 

C  —  Thick  tabular,  square  Vitreous 

brown 

(Ce,La,Di)P04 

prismatic 

Transparent 

Yellowish 

M  —  Angular    fragments,     to  opaque 

brown 

rolled  grains 

Honey  yellow 

272 

Caricrinite 

Hexagonal 

Greasy 

Yellow 

C  —  Prismatic,  rare 

Vitreous 

Brownish 

H6(Na2,Ca)4(NaC03)2- 

M  —  Compact,     lamellar,   Pearly 

yellow 

Al8Si9O36 

columnar,     dissemi-  Translucent 

nated 

to  trans- 

. 

302 

parent 

BRONZITE  (Pyroxene) 

Orthorhombic 

Bronzy 

Bronze 

C  —  Prismatic,  rare 

Silky 

brown 

(Mg,Fe)2(Si03)2 

M  —  Fibrous,  lamellar, 

Translucent 

Yellowish 

compact 

to  opaque 

brown 

304 


4.  YELLOW  OR  BROWN  IN  COLOR 


507 


Hardness  3  to  6 

Cleavage 
Streak                 Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

5.          White                      C  —  Rhombohedral,        4.1 
Gray                             not    often    ob-       4.5 
served 
F  —  Uneven, 
splintery 
Brittle 

Cellular  varieties  called 
dry  bone.  Often  mixed 
with  sand,  clay,  limonite, 
calcite.  With  zinc  miner- 
als, especially  sphalerite, 
hemimorphite.  F  r  e- 
quently  pseudomorphous 
after  calcite. 

6.         White                     C  —  Prismatic,   per-       2.2 
5.6                                            feet                           2  .  3 
F  —  Uneven 
Brittle 

Crystals  have  nearly 
square  cross-section.  In 
basalts  and  phonolites. 
With  chabazite,  analcite, 
apophyllite,  stilbite,  dato- 
lite. 

6.         White                     C  —  Prismatic,  con-       3.4 
6.6       Gray                             spicuous,   part-       3.6 

With  feldspars,  pyroxenes, 
amphiboles,  chlorite, 

ing  often  noted 
F — Conchoidal 
Brittle 


scapolite,  zircon. 


6.         White  , 
6.5 


C— Basal 

F — Conchoidal,  un- 
even 
Brittle 


4.9  Crystals  commonly  small, 
5.3  highly  modified;  rounded 
grains  in  sand.  With 
quartz,  magnetite,  zircon, 
garnet,  gold  chromite, 
diamond. 


5. 
6. 


White 


C — Prismatic  2.4      Easily  recognized  by  asso- 

F — Uneven  2 . 5        ciates — nephelite,  s  o  d  a- 

Brittle  lite,  biotite,   feldspar, 

titanite. 


5.  White  C— Prismatic,  pina- 

6.  Grayish  coidal,  conspic- 

uous 

F — Uneven 
Brittle 


3.2  Cleavage  surfaces  usually 
3 . 5  fibrous  or  lamellar,  irregu- 
lar or  wavy,  with  distinct 
bronzy  luster;  darker  than 
enstatite.  In  basic  igne- 
ous rocks. 


508 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

RHODONITE  (Pyroxene)       Triclinic  Vitreous  Yellowish 

C — Tabular,  prismatic  Dull  Brownish 

MnSiOs  rounded  edges  Translucent 

M — Cleavable,  to  opaque 

granular,  dissemi- 
309  nated  grains 


Willemite  (Troostite) 
Zn2SiO4 

289 


Hexagonal  Greasy  Yellow 

C — Prismatic  Vitreous  Greenish 

M — Compact,    granular,  Transparent  yellow 

disseminated  grains      to  opaque  Brown 


OPAL,  varieties  Amorphous  Vitreous  Yellow 

Precious  opal     M — Compact,    reniform,   Greasy  Yellowish 
SiO2.xH2O  Wood  opal                 botryoidal,     porous,   Dull  brown 

Opal  jasper  earthy  Translucent  Brown 

Silicious  sinter  to  opaque 

232  Tripolite 

Streak — Uncolored,  white,  or  light  gray 

ORTHOCLASE  (Feldspar)     Monoclinic  Vitreous  Pale  yellow 

C — Prismatic,  thick  tab-  Pearly  Brownish 

KAlSi3O8  ular;     twins;     often  Translucent       yellow 

large  to  opaque 
M — Cleavable,  granular, 
316                                            disseminated 


Chondrodite 


[Mg(F,OH)]2Mg3(Si04); 


286 


Monoclinic  Vitreous  Reddish 

C — Small,   highly  modi-  Greasy  brown 

fied,  rare  Translucent  Yellowish 

M — Disseminated  grains,  -  to  opaque         brown 

compact  Honey  yellow 


Sillimanite  (Fibrolite) 
Al2SiO6 


Orthorhombic  Vitreous  Hair  brown 

C — Long,    thin,    needle-  Silky  Grayish 

like  Transparent       brown 
M — Fibrous,     columnar,     to  trans- 
radiating  lucent 


282 


4.  YELLOW  OR  BROWN  IN  COLOR 


509 


Hardness  3  to  6 

1 

Strea 
ness 

Cleavage  =  C 
k                  Fracture   =  F 
Tenacity 

eific          Characteristics  and 
vity                 Associates 

6.         White 
6. 

C  —  Prismatic,  basal       3  .  4      On  exposure      may       be 
F  —  Conchoidal,  un-        3  .  7        stained  brown  or  black, 
even                                        Fowlerite,    contains    zinc. 
Tough,                                           With  franklinite,  zincite, 
crystals  brittle                     willemite,     calcite,    iron 
ores. 

6.         White 
6. 

C  —  Basal,  prismatic       3  .  9      Crystals  of  willemite  small, 
F  —  Uneven                     4.3       of  troostite,  manganifer- 
Brittle                                          ous  variety,  often  large. 
Characterized    by    asso- 
ciates —  franklinite,     zinc- 
ite, rhodonite,  calcite. 

6.6       White 
6. 

F  —  Conchoidal,              2  .  1      Precious  opal,   play  of 
conspicuous              2.3        colors;  wood  opal,  woody 
when  compact;                     structure;  opal  jasper, 
earthy                                    greasy,  resembling  jasper; 
Brittle                                         silicious    sinter,    porous; 
tripolite,  earthy,  gritty. 

Hardness  over  6 

6.         White 
6.6 

C  —  Basal  clinopin-        2.5      Characterized   by   rectan- 
acoidal,    con-       2.6       gular  cleavages  and  ab- 
spicuous  —  90°                      -sence  of  twinning   stria- 
F  —  Conchoidal,  un-                    tions.     In  granitic  rocks, 
even                                       With  quartz,  other  feld- 
Brittle                                           spars,  mica,  hornblende. 

6.         White 
6.6 

C  —  Basal,  indistinct       3 
F  —  Conchoidal,  un-       3 
even 
Brittle 

.  1      Associates  important.     In 
.  3        crystalline  limestones  and 
dolomites.     With    spinel, 
ves\ivianite,      pyroxenes, 
mica. 

6.         White 
7. 

C  —  Macropina-              3.2      Crystals  often  slender, 
coidal                        3.3        bent,     striated,     with 
F  —  Uneven                                 rounded    edges,    without 
Brittle                                         good    terminations,    and 
interlaced.     In  metamor- 
phic   rocks  —  mica,  schist, 
gneiss.     With  andalusite, 
garnet. 

510 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster                  ~  , 
m                                Color 
Transparency 

EPIDOTE                                  Monoclinic                           Vitreous            Greenish 
C  —  Prismatic,    elongated  Transparent       brown 
Ca2(Al,Fe)2(Al.OH)(SiO4)3         and  deeply  striated     to  opaque       Greenish 
parallel    to    b    axis;                              yellow 
usually     terminated                            Yellow 
on  one  end  only 
M  —  Columnar  ;     fibrous, 
parallel    and    diver- 
286                                              gent;  granular 

RUTILE 
TiO2  or  TiTiO4 

224 

Tetragonal                           Adamantine    Reddish 
C  —  Prismatic,    vertically  Submetallic        brown 
striated;      twinned,   Translucent    Yellowish 
yielding  knee-shaped     to  opaque         brown 
or  rosette  forms                                  Dark  brown 
M  —  Compact,  dissemi- 
nated 

CASSITERITE 

SnO2  or  SnSnO4 

226 

Tetragonal 
C  —  Thick  prismatic; 
knee-shaped  twins 
quite  common 
M  —  Reniform,  botry- 
oidal,  compact, 
rounded  pebbles, 
often   with   interna] 
radial,  fibrous  struc- 
ture, wood  tin 

Adamantine      Reddish 
Greasy                brown 
Dull                   Yellowish 
Translucent        brown 
to  opaque        Dark  brown 

VESUVIANITE 

Ca6[Al(OH,F)]Al2(SiO4)5 

288 

Tetragonal 
C  —  Short  prismatic 
M  —  Compact,    granular, 
aggregates  with  par- 
allel    or     divergent 
striations  or  furrows 

Vitreous            Brown 
Greasy              Greenish 
Translucent        brown 
to  opaque       Sulphur 
yellow 

GARNET,  varieties                  Cubic 
Grossularite  C  —  Dodecahedrons,      te- 
R3"R2'"-           Spessartite            tragonal    trisoctahe- 
(SiO4)s          Almandite             drons,    alone    or    in 
R"  =  Ca,-        Andradite             combination 
Fe,Mg,Mn                          M  —  Granular,    compact, 
R'"  =  Al,Fe                                 lamellar,  dissemi- 
nated grains,  sand 

Vitreous            Yellow 
Transparent     Cinnamon 
to  opaque         brown 
Reddish 
brown 

290 


4.  YELLOW  OR  BROWN  IN  COLOR 


511 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.          White                      C  —  Basal                         3  .  3      Crystals  often  darker  than 
7.         Grayish                  F  —  Uneven                     3  .  5       when    massive.     With 
Brittle                                         quartz,     feldspar,     vesu- 

vianite,  hornblende,  py- 
roxenes, magnetite,  na- 
tive copper. 


6.  Gray  C — Prismatic,    py- 

7.  Yellowish  white  ramidal,    not 
Brownish  white  conspicuous 

F — Uneven 
Brittle 


4 . 2  Not  as  heavy  as  cassiterite. 

4.3  Often  in  fine  hair-like  in- 
clusions.    With  quartz, 
feldspar,  hematite,  ilmen- 
ite,  chlorite. 


6.  White  C— Indistinct  6.8 

7.  Yellowish  white     F — Uneven  7 . 
Brownish  white     Brittle 


Distinguished  by  high  spe- 
cific gravity.  In  veins 
cutting  granite,  gneiss;  in 
alluvial  deposits  as  stream 
tin.  With  quartz,  wol- 
framite, scheelite,  moly- 
bdenite, tourmaline,  fluor- 
ite,  mica,  chlorite. 


6.5       White 


C — Indistinct  3.3      In    crystalline    limestone, 

F — Uneven  3 . 5        gneiss,  schist.     With  gar- 

BrittJe  net,    tourmaline    chond" 

rodite,   wollastonite,   epi- 
dote,  pyroxenes. 


6.5 
7.6 


White 


C — Dodecahedral, 
usually  indis- 
tinct 

F — Conchoidal,  un- 
even 

Brittle 


3.4  Grossidarite ,  in  crystalline 
4.3  limestone,  dolomite,  with 
wollastonite,  vesuvianite, 
diopside,  scapolite ;  spes- 
sartite,  in  granitic  rocks, 
with  quartz,  tourmaline, 
orthoclase;  almandite, 
with  mica,  staurolite, 
andalusite,  cyanite;  and- 
radite,  with  epidote,  feld- 
spar, nephelite,  leucite. 


512 


B.     MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

QUARTZ,  Phanerocrystal-      Hexagonal 


Vitreous 


line  varieties       C — Prismatic,    horizont-  Greasy 
SiO2  Smoky  quartz          ally  striated  Transparent 

False  topaz       M — Compact,  granular        to  opaque 
Aventurine 
Ferruginous 
Cat's  eye 


Yellow 
Yellowish 

brown 

Smoky  brown 
Reddish 

brown 


222 


Cryptocrystalline  Hexagonal  Waxy  Yellow 

varieties  C — Never  in  crystals  Vitreous  Brown 

Chalcedony       M — Nodular,  botryoidal,  Translucent  Blackish 

Agate  banded,    concretion-  to  opaque  brown 

Jasper  ary,  stalactitic,  com- 

Flint  pact 


223 


Clastic  varieties 

Hexagonal 

Vitreous 

Yellow 

Sand 

M  —  Grains,  fragments, 

Dull 

Yellowish 

Sandstone 

either  loose  or 

Translucent 

brown 

Quartzite 

strongly  consoli- 

to opaque 

Brown 

dated 

224 


TOURMALINE 

M'9Al3(B.OH)2Si4019 
M'  =  Na,K,Li,Mg,Fe 


Hexagonal  Vitreous  Brown 

C — Prismatic,    vertically  Translucent  Yellowish 

striated;  terminated     to  opaque  brown 

with  broken  or  rhom-  Yellow 
bohedral-like  surfaces 
M — Compact,  granular 


284 


4.     YELLOW  OR  BROWN  IN  COLOR 


513 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

/^ 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

7.          White  C — Indistinct 

Yellowish  white     F — Conchoidal, 
Brownish  white  conspicuous 

Brittle 


2 . 6  Characteristic  conchoidal 
fracture  and  glassy  luster. 
Smoky  quartz,  smoky  yel- 
low to  brownish  black; 
false  topaz,  yellow;  aven- 
turine,  glistening  with  in- 
cluded scales ;  ferruginous,  ^ 
colored  by  iron  oxide, 
cat's  eye,  opalescent,  due 
to  inclusions  of  fibers  of 
asbestos. 


7.         White  C — Indistinct 

Yellowish  white     F — Conchoidal, 
Brownish  white  conspicuous 

Brittle  to  tough 


2.6  Not  as  glassy  as  phanero- 
crystalline  varieties. 
Chalcedony,  pale  to  dark 
brown,  waxy  luster;  agate, 
banded  or  clouded;  jasper, 
commonly  yellow  and  uni- 
form in  color ;  flint,  smoky 
or  blackish  brown,  nodu- 
lar, often  with  white 
coating. 


7.          White  C — Indistinct  2.6      Pigment  is  usually  ferru- 

Yellowish  white     F — Uneven  ginous   matter.     Sand, 

Brownish  white     Brittle  to  tough  loose,    unconsolidated 

grains;  sandstone,  consoli- 
dated sand ;  quartzite, 
metamorphosed  s  a  n  d- 
stone. 


7. 
7.5 


White 


C — None 

F — Conchoidal,  un- 
even 
Brittle 


2.9  Spherical,  triangular  cross- 
3.2  section.  Commonly  as 
contact  mineral  in  granu- 
lar limestone  and  doio- 
m  i  t  e.  With  tremolite, 
scapolite,  vesuvianite, 
apatite,  garnet,  spinel. 


514 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Cry  stalliz  ation 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

STAUROLITE  Orthorhombic  Vitreous  Reddish 

C — Prismatic ;  twins  plus-  Dull  brown 

Fe(AlO)4(Al.OH)(SiO4)2  (+)    or    X-shaped;  Translucent      Yellowish 

well  developed  to  opaque         brown 

Blackish 
brown 


279 
ZIRCON 

ZrSiO4 
225 


Tetragonal  Adamantine  Reddish 

C — Square    prisms    and  Vitreous  brown 

bipyramids,      small,  Greasy  Dark  brown 

well  developed  Transparent  Brownish 

M — Irregular  lumps,  to  opaque  yellow 

grains 


BERYL 

Be3Al2(Si03)6 

313 


Hexagonal  Vitreous  Pale  yellow 

C — Long  prismatic,  often  Transparent  Honey  yellow 

vertically  striated,         to  trans-  Brownish 

large  lucent  yellow 
M — Columnar,  granular, 
compact 


SPINEL,  varieties                    Cubic                                   Vitreous  Yellow 

Pleonaste  C — Octahedral,  well  de-  Dull  Grayish 

R"(R'"O2)2          Gahnite             veloped                         Nearly  brown 

R"  =  Mg,Fe,Zn                   M — Compact,    granular,     opaque  Brown 
R'"  =  Al,Fe                                 disseminated  grains 


267 


TOPAZ 

Al2(F,OH)2Si04 


Orthorhombic  Vitreous  Straw  yellow 

C — Prismatic,     vertically  Transparent  Wine  yellow 

striated,  highly  to  opaque  Yellowish 

modified  brown 
M — Compact,    granular, 
rolled  fragments 


283 


4.  YELLOW  OR  BROWN  IN  COLOR 


515 


Hardness  over  6 


Cleavage  =  C        ~ 
HMd-             Streak                  Fracture  =  F 
ness                                           Tenacity 

;ific          Characteristics  and 
rity                 Associates 

7.          White                      C  —  Brachypina-             3  .  4      Fresh  crystals  usually  pos- 
7.6        Grayish                         coidal                        3.8        sess  bright,  smooth  faces, 
F  —  Conchoidal,  un-                     when  altered  dull,  rough, 
even                                        softer   and   with    colored 
Brittle                                           streak.     In  metamorphic 
rocks  —  g  neiss,   mica 
schist,  slate.     With  cyan- 
ite,    garnet,    tourmaline, 
sillimanite 

7.5        White                      C  —  Indistinct                  4.4      In  the  more  acid  igneous 
F  —  Uneven                      4.8        rocks  —  granite,      syenite; 
Brittle                                           alluvial   deposits,   with 
gold,    spinel,    corundum, 
garnet.     Hyacinth,     clear 
and  transparent. 

7.5        White                      C  —  Basal,  indistinct 
8.                                        F  —  Conchoidal,  un- 
even 
Brittle 

2.6      Crystals    usually    simple* 
2  .  8        prism  and  base.     In  gran- 
itic  rocks,   mica  schists, 
clay  slates.     With  quartz, 
feldspar,     mica,     ehryso- 
beryl,    topaz,    cassiterite, 
garnet. 

7.5        White                      C—  Indistinct 
8.          Grayish                   F  —  Conchoidal 
Brittle 

3  .  6      Commonly  as  contact  min- 
4  .  4        eral  in  granular  limestone  ; 
in    more    basic     igneous 
rocks;  as  rounded  grains 
in  placers.     With  calcite, 
chondrodite,     serpentine, 
brucite,  graphite,  pyrox- 
enes. 

White 


C — Basal,  perfect, 
conspicuous 

F — Conchoidal,  un- 
even 

Brittle 


3 . 4  Crystals  usually  developed 
3.6  on  one  end  only.  Color 
may  fade  on  exposure. 
Massive  varieties  disting- 
guished  from  quartz  by 
higher  specific  gravity  and 
basal  cleavage.  In  veins 
and  cavities  in  granitic 
rocks,  also  in  placers. 
With  cassiterite,  tourma- 
line, fluorite,  apatite, 
beryl,  wolframite. 


516 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Chrysoberyl 

Be(A102)2 

271 


Orthorhombic  Vitreous  Yellow 

C — Tabular;  heart-  Greasy  Greenish 

shaped,  pseudohex-  Transparent       yellow 

agonal  twins  to  trans-  Brown 

M — Fragments,  loose,  lucent 
rounded  grains 


CORUNDUM,  varieties  Hexagonal  Vitreous  Yellow 

Oriental    C — Prismatic,  tabular,       Translucent      Brown 
A12O3  topaz  pyramidal,  rhombo-      to  trans- 

Common  hedral;  rough  or  parent 

rounded  barrel- 
shaped 

M — Compact,    granular, 
228  lamellar 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Cerargyrite  (Horn  silver) 
AgCl 


238 


Cubic  Waxy  Pearl  gray 

C — Rare  Greasy  Grayish 

M — Wax-like  crusts,  Transparent 
coatings;  stalactitic,     to  trans- 
dendritic  lucent 


Asbestos,  variety 

Orthorhombic  ?                   Silky 

White 

Chrysotile 

M  —  Coarse  or  fine  fibrous,  Silky 

Greenish 

H4Mg3Si209 

felted                              metallic 

white 

Opaque 

Yellowish 

white 

298 

variety 

Monoclinic  ?                         Silky 

White 

Amphibole 

M  —  Coarse  or  fine  fibrous,  Dull 

Greenish 

Silicate  of  Ca,  Mg,  Fe,  Al, 

felted;  compact,           Opaque 

white 

etc. 

leather-  or  cork-like 

Yellowish 

white 

311 


4.  YELLOW  OR  BROWN  IN  COLOR 


517 


Hardness  over  6 


**ld-            Str 

ness 

Cleavage  =  C 
eak                  Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

8.6        White 

C  —  Brachypina- 

3.5 

Crystals    disseminated    as 

coidal 

3.8 

plates,  often  with  feather- 

F  —  Uneven,    c  o  n- 

like   or   radial  striations. 

choidal 

In  granite,  gneiss,  placers. 

Brittle 

With  beryl,  garnet,  tour- 

maline, sillimanite. 

9.          White 

C  —  None,  nearly 

3.9 

When  massive  often  multi- 

rectangular 

4.1 

colored  —  red,  blue,  green, 

basal  and  rhom- 
bohedral    part- 
ings,   conspicu- 
ous; striated 
F— Conchoidal 
Brittle  to  tough 


gray.  Oriental  topaz, 
transparent,  yellow.  In 
limestone,  granite,  syen- 
ite, alluvial  deposits. 
With  magnetite,  nephel- 
ite,  mica,  spinel,  chlorite. 


6.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


Hardness  1  to  3 


1.          White,  shiny          C — None  5.5      Cuts    like    wax;    on     ex- 

1.6        Gray,  shiny  F — Conchoidal  5 . 6       posure   turns   violet, 

Highly  sectile  brown,    or   black.     With 

silver       minerals;       also 
limonite,  calcite,  barite. 


1. 
2.5 


White 


F — Fibrous 
Flexible 


1 .  Short  fibered  asbestos,  deli- 
2 . 5  cate,  fine,  parallel,  flexible 
fibers,  easily  separable, 
perpendicular  to  walls. 
Compare  below.  In  veins 
or  seams  in  serpentine. 


1. 
2.5 


White 


F — Fibrous  1.        Long  fibered  asbestos,  par- 

Flexible,  tough  2.5        allel,   flexible  fibers,  par- 

allel to  walls.  Mountain 
leather,  mountain  cork, 
mountain  wood,  compact, 
but  light  and  tough. 


518 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

TRIPOLITE  (Opal)                  Amorphous                           Dull                   Gray 
M  —  Porous,  earthy,            Opaque             White 
SiO2.xH2O                                    chalk-like                                              Yellowish 
white 

234 


KAOLINITE  (Kaolin,  china 

Monoclinic 

Dull 

White 

clay) 

C  —  Scaly,  rare 

Pearly 

Gray 

H4Al2Si2O9 

M  —  Compact,  friable, 

Opaque  to 

Colorless 

mealy,  clay-like 

translucent 

301 

CALCITE,  varieties 

Hexagonal 

Earthy 

White 

Chalk 

M  —  Loose    or    compact, 

Dull 

Grayish 

CaCO3        Marl 

earthy 

Opaque 

Yellowish 

white 

244 

TALC,  varieties  Monoclinic  Pearly  White 

Foliated  C — Thin   tabular,    indis-  Greasy  Greenish 

Soapslone  or  steatite          tinct  Transparent  white 

French  chalk  M — Foliated,  globular,        to  opaque  Gray 

H2Mg3Si4Oi2  fibrous,  granular, 

compact 


299 


BAUXITE 
A12O(OH)4 


Never  in  crystals  Dull 

M — Pisolitic,  oolitic,  Earthy 

rounded  dissemi-         Opaque 
nated   grains ;   clay- 
like,  earthy 


White 
Grayish 


235 


6.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


519 


Hardness  1  to  3 


Hard- 
ness 

Streak 

' 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

1.          White                      F  —  Earthy                       2  .  1      Apparently  very  soft,  but 
2.5                                       Friable                             2  .  3        fine  particles  scratch 

glass.  Resembles  chalk 
and  kaolinite,  but  gritty, 
and  not  plastic  when 
moistened.  Due  to  im- 
purities may  have  clay 
odor. 


1.          White                      C  —  Basal  (scales) 
2.6                                       F—  Earthy 
Brittle 

2.2      Not   gritty   like   tripolite. 
2.6        Very    strong    clay    odor 
when    breathed    upon. 
Usually  adheres  to  tongue 
and  becomes  plastic  when 
moistened.     Greasy   feel. 
With     quartz,     feldspar, 
corundum. 

1.         White                     C—  None 
2.5                                       F—  Earthy 
Brittle 

2  .  7      Chalk,  earthy  masses  ;  marl, 
more    clay-like    and    fre- 
quently contains  organic 
material  —  leaves,      twigs. 
In  extensive  deposits. 

1.          White                      C  —  Basal,   conspic- 
2.5                                              uous,  when  fol- 

2.6      Greasy  or  soapy  feel  im- 
2.8        portant.     Foliated  talc, 

iated 
F — Uneven, 

splintery 
Sectile,  laminae 

flexible 


easily  separable,  inelastic 
folia  or  plates,  H  =  1; 
soapstone  or  steatite,  coarse 
to  fine  granular,  rather 
impure,  H  =  1.5 — 2.5; 
French  chalk,  soft,  com- 
pact, marks  cloth  dis- 
tinctly. With  serpentine, 
dolomite,  chlorite,  mag- 
nesite,  actinolite. 


White 


F— Earthy 
Brittle 


2.5  Clay  odor  when  breathed 
upon.  Usually  distin- 
guished from  clay  by 
pisolitic  or  oolitic  struc- 
ture. With  clay  or  kaolin 
in  nodules,  grains,  or  ir- 
regular masses  in  lime- 
stone or  dolomite. 


520 


B.     MINERALS  WITH  NON-METALLIC  LUSTER 


Streak— Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

SODA  NITER   (Chile  salt-  Hexagonal  Vitreous  Colorless 

peter)   C — Similar   to    those    of  Transparent     White 
NaNO3                                         calcite,  rare  Grayish 

M — Granular,  crusts, 
241  efflorescences 

GYPSUM,  varieties  Monoclinic  Pearly  Colorless 

Selenite       C — Tabular,    prismatic;  Vitreous  White 

CaSO4.2H2O      Satin  spar          swallow-tail  twins  Silky  Gray 

Alabaster     M — Cleavable,  coarse  or  Dull 

Common  fine  grained,  fibrous,  Transparent 

foliated,  earthy  to  opaque 


264 


Melanterite  (Copperas) 
FeSO4.7H2O 

Monoclinic 
C—  Rare 
M  —  Capillary,  fibrous, 
stalactitic,  concre- 
tionary, powder 

Vitreous            White 
Dull                  Greenish 
Transparent       white 
to  trans-          Yellowish 
lucent               white 

266 


Sepiolite  (Meerschaum) 
H4Mg8Si»Oio 

Monoclinic  ? 
M  —  Compact,  nodular 
with  smooth  feel; 
earthy,  clay-like 

Dull 
Opaque 

White 
Grayish  white 

300 


Epsomite  (Epsom  salt) 
MgSO4.7H2O 
265 

Orthorhombic 
C  —  Prismatic,  nearly 
square,  rare 
M  —  Granular,  fibrous, 
earthy,  crusts 

Vitreous            White 
Dull                   Colorless 
Transparent     Gray 
to  trans- 
lucent 

HALITE  (Rock  salt) 
NaCl 

236 

Cubic 
C  —  Cubes,  often  skeletal 
or  hopper-shaped 
M  —  Compact,  cleavable, 
granular,  fibrous, 
stalactitic,  crusts 

Vitreous            Colorless 
Transparent     White 
to  trans-          Grayish 
lucent 

6.     COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


521 


Hardness  1  to  3 


Cleavage  =  C 
Streak                  Fracture  =  F        f?* 
ness                                           Tenacity 

cific          Characteristics  and 
vity                 Associates 

1.5        White                      C  —  Rhombohedral         2.1      Cooling   and  saline   taste. 
2.                                         F  —  Conchoidal               2  .  3        Absorbs  moisture  readily. 
Brittle                                           In  extensive  deposits. 
With  gypsum,  sand,  clay, 
guano. 

1.6        White                      C  —  Clinopinacoidal,       2  .  2      Selenite,  crystals  and  cleav- 
2.                                                conspicuous;             2.4        age  plates,  usually  trans- 
pyramidal,    or-                     parent;  satin  spar,  fibrous 
thopinacoidal                       with    silky    luster;    ala- 
F  —  Conchoidal,                           hosier,  granular.     In  lime- 
fibrous                                   stones,  shales.     With  hal- 
Brittle,  laminae                            ite,  celestite,  sulphur,  ara- 
flexible                                   gonite,       dolomite,      ore 
deposits. 

2.          White                      C—  Basal                          1 
F  —  Conchoidal,               1 
earthy 
Brittle 

.8      On    exposure    loses    water 
.9       and  crumbles.     Sweet, 
astringent  taste,  s  o  m  e- 
what  metallic.    Oxidation 
product  of  iron  sulphide 
minerals  —  marcasite,   py- 
rite,     chalcopyrite, 
pyrrhotite. 

2.          White                      C  —  None                          1.         Recognized  by  smooth  feel, 
2.6                                       F  —  Conchoidal,  un-        2.          adherence  to  tongue,  low 
even                                      specific  gravity  and  lack 
Brittle                                        of   clay   odor   when 
breathed  upon.     Im- 
pressed   by    finger     nail. 
With  serpentine,  magne- 
site,  chlorite. 

2.          White                      C  —  Brachypina-             1 
2.6                                            coidal                        1 
F  —  Conchoidal 
Brittle 

.  7      Non-hygroscopic.      Bitter, 
.  8       salty  taste.     In  limestone 
caves.     With  serpentine, 
talc,  magnesite. 

2.          White                      C—  Cubic,    perfect,        2 
2.6                                              conspicuous              2 
F  —  Conchoidal 
Brittle 

.  1      May  absorb  moisture  and 
.3       become    damp.     Charac- 
teristic   cubical   cleavage 
and    saline    taste.     With 
slate,  gypsum,  anhydrite. 

522 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Lepidolite  Monoclinic  Pearly  White 

C — Short  prismatic  Translucent      Pinkish  white 
(Li,H)2(F.OH)2Al2-       M — Coarse  or  fine  granu-  Lavender 

Si3O9  lar,  scales,  cleav-  Gray 

able  plates 
297 


MUSCOVITE  (Isin-         Monoclinic 


Vitreous 


H2KAl3(SiO4)j 


glass)   C — Tabular,    pyramidal,   Pearly 


Colorless 
Yellowish 

with     orthorhombic  Transparent       white 
or    hexagonal     out-     to  trans-          Brownish 
line;  often  large  and     lucent  white 

rough 

M — Scales,    plates;   foli- 
ated   and    plumose 


295 


APATITE,  variety  Hexagonal  Dull 

Phosphate  rock  M — Compact,  fibrous,        Opaque 
Ca6F(PO4)3,  chiefly  nodular,  reniform, 

earthy 
273 


White 
Gray 


CRYOLITE 
AlF3.3NaF 

240 


Monoclinic  Vitreous  Snow  white 

C — Small,  pseudocubical  Greasy  Gray 

rare  Pearly  Colorless 

M — Cleavable,  compact,  Transparent 

granular  to  trans- 

lucent 


BARITE  (Heavy  spar) 
BaSO4 


Orthorhombic  Vitreous  Colorless 

C — Tabular,  prismatic;  Pearly  White 

crested  divergent  Transparent     Gray 

groups  to  trans- 

M — Compact,  cleavable,  lucent 

lamellar,  fibrous, 

reniform 


256 


6.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


523 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

2.          White                      C  —  Basal,  perfect           2.8      When    massive    often    re- 
3.                                         F  —  Scaly  granular          2  .  9        sembles     granular     lime- 
Tough                                           stone.     In  pegmatites, 

granites,  gneisses.  With 
red  tourmaline  (rubellite), 
spodumene,  cassiterite. 


White 


C — Basal,    perfect, 
conspicuous 

Tough,  laminae 
very  elastic 


2.8  Structure,  perfect  cleav- 
3 . 1  age,  and  elasticity  im- 
portant. Large  crystals 
often  show  distinct  part- 
i  n  g  s  perpendicular  to 
cleavage,  ruled  mica.  In 
granitic  rocks,  schists, 
limestones.  With  f  e  1  d- 
spar,  quartz,  beryl,  tour- 
maline, garnet,  spodu- 
mene. 


2.          White                      F  —  Conchoidal,  un- 
3.                                                even 
Brittle 

3  .  1      More   or   less   impure 
3.2        masses,  frequently  re- 
sembling   compact    lime- 
stone.   Independent  beds, 
nodules,  concretions. 

2.6       White                     C—  Basal,  pris- 
3.                                                matic,  nearly  at 
90°;  sometimes 
conspicuous 
F  —  Uneven 
Brittle 

2  .  9      Frequently  resembles  snow 
3.          ice.     Often  contains  dis- 
seminated  siderite,    chal- 
copyrite,    galena,    pyrite, 
fluorite,  columbite. 

2.6       White                     C—  Basal,  pris- 
3.                                                matic,  con- 
spicuous 
F  —  Uneven 
Brittle 

4.3      Characterized    by    rather 
4.7        high  specific  gravity  and 
cleavages.     In  metallifer- 
ous   veins;    pockets    and 
lenticular  masses  in  lime- 
stones.    With  galena, 
sphalerite,   fluorite,   chal- 
copyrite;  manganese  and 
iron  ores. 

524 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CALCITE,  varieties 

Dog  tooth  spar 


CaC05 


242 


Nail  head  spar 
Iceland  spar 
Satin  spar 
Limestone 
Coquina 
Marble 

Calcareous  tufa 
Travertine 
Stalactites,  etc. 


Hexagonal  Vitreous  White 

C — Scalenohedral,  rhom-  Dull  Grayish 

bohedral,  prismatic,  Transparent     Colorless 


tabular,  acicular; 
highly  modified; 
twins 

M — Cleavable,  granular, 
fibrous,  banded,  stal- 
actitic,   oolitic,  por- 
ous, compact,  crusts 
shells 


to  nearly 
opaque 


Streak — Uncolored,  white,  or  light  gray 


ANHYDRITE 

CaS04 

254 


Orthorhombic  Vitreous  White 

C — Thick   tabular,   pris-  Pearly  Bluish  white 

matic,  rare  Transparent  Reddish  white 

M — Granular,    compact,  to  trans-  Grayish 

fibrous,      cleavable,  lucent 

lamellar,  reniform 


CELESTITE 

SrSO4 

255 


Orthorhombic  Vitreous  Colorless 

C — Tabular,  prismatic,  Pearly  White 

common;  pyramidal  Transparent     Gray 
M — Compact,  cleavable,     to  trans- 
fibrous,  granular,  lucent 
reniform 


BARITE  (Heavy  spar) 
BaS04 


Orthorhombic 

C — Tabular,  prismatic; 

crested  divergent 

groups 
M — Compact,  cleavable, 

lamellar,  fibrous, 

reniform 


Vitreous  Colorless 

Pearly  White 

Transparent     Gray 
to  trans- 
lucent 


256 


5.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


525 


Hardness  1  to  3 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.          White 


C — Rhombohedral, 
perfect,  usually 
conspicuous 

F — Conchoidal 

Brittle 


2 . 7  Rhombohedral  cleavage 
characteristic,  especiaDy 
on  crystals.  Cleavage 
surfaces  often  striated. 
Very  strong  double  re- 
fraction easily  observed 
when  transparent.  To 
distinguish  varieties,  see 
reference. 


Hardness  3  to  6 


3.         White 
3.5 


C  —  Pinacoidal,  3  di-      2.7      Pseudocubical        cleavage 


rections  at  90°, 
sometimes  con- 
spicuous 

F  —  Conchoidal 

Brittle 


3.  sometimes  noted.  Gran- 
ular  varieties  resemble 
marble.  Not  as  heavy 
as  celestite  or  barite. 
With  halite,  gypsum. 


3. 
3.5 


White 


C — B  a  s  a  1,  pris- 
matic, conspic- 
uous 

F — Uneven 

Brittle 


3.9  Usually  with  faint  bluish 
4.  tinge.  Heavier  than  cal- 
cite,  anhydrite;  lighter 
than  barite.  Good  cleav- 
ages. In  limestones,  dolo- 
mites, shales.  With  sul- 
phur, gypsum,  aragonite, 
halite,  galena,  sphalerite. 


3. 
3.5 


White 


C — B  a  s  a  1,  pris- 
matic, conspic- 
uous 

F — Uneven 

Brittle 


4.3  Characterized  by  rather 
4.7  high  specific  gravity  and 
cleavages.  In  metallifer- 
ous veins;  pockets  and 
lenticular  masses  in  lime- 
stones. With  galena, 
sphalerite,  fluorite,  chal- 
copyrite;  manganese  and 
iron  ores. 


526 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

ANGELSITE 
PbSO4 


Orthorhombic  Adamantine      Colorless 
C — Prismatic,  tabular,  Greasy  White 
pyramidal  Transparent     Gray 
M — Compact,    granular,     to  trans- 
nodular  lucent 


257 


CERUSSITE 

Orthorhombic 

Adamantine 

Colorless 

C  —  Tabular,  prismatic, 

Greasy 

White 

PbCO7 

pyramidal;  pseudo- 

Silky 

Gray 

hexagonal;  clusters 

Transparent 

and  star-shaped 

to  trans- 

groups 

lucent 

251 


M — Interlaced  bundles, 
granular,  stalactitic, 
compact 


STILBITE  (Zeolite)  Monoclinic  Vitreous  White 

C — Twinned,    sheaf-like,   Pearly  Yellowish 

(Ca,Na2)Al2Si6Oi6.6H2O9  radial,    or    globular  Transparent       white 

aggregates  to  trans- 

lucent 
326 


Lepidolite  (Mica) 

(Li,H)2(F,OH)2Al2Si309 


297 


Monoclinic  Pearly  White 

C — Short  prismatic  Translucent      Pinkish  white 

M — Granular,   coarse  or  Lavender 

fine ;  scales,  cleavable  Gray 

plates 


PHOSPHATE  ROCK 

(Apatite) 
Ca6F(PO4)3,  chiefly 


Hexagonal  Dull  White 

M — Compact,  fibrous,        Opaque  Gray 

nodular,  renit'orm, 

earthy 


274 


6.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


527 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 

Associates 

3.          White                     C  —  B  a  s  a  1,    pris-        6  .  1      Luster  and  very  high  spe- 
3.6                                              matic                         6.4        cific    gravity    important. 
F  —  Conchoidal                             Distinguished  from  cerus- 
Brittle                                         site  by  absence  of  twins 

Oxidation  product  of  lead 
minerals.  Usually  in 
cracks  and  cavities,  with 
galena,  cerussite. 


3.          White                      C  —  Indistinct 
3.6                                      F  —  Conchoidal 
Brittle 

6  .  4     Twinning,  structure,  luster, 
6.6        arid  specific  gravity  char- 
acteristic.    With    lead 
minerals  —  galena,  pyro- 
morphite,   ariglesite;  also 
malachite,  limonite. 

White 


C — Pinacoidal  2 . 1      Radial  or  sheaf-like  struc- 

F — Uneven  2.2       ture.     In    basic    igneous 

Brittle  rocks;  ore  deposits.    With 

chabazite,       apophyllite, 
datolite,   calcite. 


White 


C — Basal,  perfect  2.8 

F — Scaly,  granular        2 . 9 
Tough 


When  massive  often  re- 
sembles  granular  lime- 
stone. In  pegmatites, 
granites,  gneisses.  With 
red  tourmaline  (rubellite), 
spodumene.  topaz. 


3.          White 
6. 


F — Conchoidal,  un-        3 . 1 
even  3 . 2 

Brittle 


More  or  less  impure 
masses,  frequently  re- 
sembling compact  lime- 
stone. Independent  beds, 
nodules,  concretions. 


528 


B.    MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

ANDALUSITE 

Al2SiO6 


Orthorhombic  Vitreous  White 

C — Prismatic,  rough,          Dull  Pearl  gray 

nearly  square,  often  Transparent     Reddish  gray 
large  without  termi-     to  opaque 
nations 

M — Columnar,    fibrous, 
granular,       dissemi- 
nated 


281 

WavelUte 
(A1.0H)3(P04)2.5H40 

276 

Orthorhombic 
C  —  Capillary,  small 
M  —  Crusts,    globular   or 
hemispherical,    with 
radial    fibrous  struc- 
ture 

Vitreous            White 
Translucent      Gray 
Colorless 

ALUNITE  (Alum  stone) 
K2(A1.20H)6(S04)4 

262 

Hexagonal 
C  —  Rhombohedrons,    re- 
sembling cubes; 
tabular,  rare 
M  —  Compact,    granular, 
fibrous,  earthy 

Vitreous            Colorless 
Pearly                White 
Transparent     Gray 
to  trans- 
lucent 

DOLOMITE 

CaMg(C03)2 

Hexagonal 
C  —  Rhombohedral    with 
curved  surfaces 
(pearl  spar) 
M  —  Coarsely  crystalline, 

Vitreous            White 
Pearly                Gray 
Transparent     Colorless 
to  trans- 
lucent 

245 
ARAGONITE 

CaC03 


249 


compact,     granular, 
friable 

Orthorhombic  Vitreous 

C — Chisel-   or  spear-  Greasy 

shaped;    pseudohex-  Transparent 
agonal  prisms;  radial,    to  trans- 
columnar,  acicular        lucent 
aggregates 
M — Branching  forms 

(flosferri),  stalactitic, 
reniform,  crusts, 
oolitic 


Colorless 

White 

Gray 


6.     COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


529 


Hardness  3  to  6 


Hard-             Str 
ness 

Cleavage  =  C        g 
eak                  Fracture  =  F 
Tenacity 

cine         Characteristics  and 
vity                 Associates 

3.  White 
6. 

C  —  Prismatic                  3  .  1      Due  to  alteration,  surface 
F  —  Uneven                     3.2       may    be     covered     with 
Brittle                                         scales  of  mica,  hence,  soft. 
Chiastolite,     regular,     in- 
t  e  r  n  a  1  arrangement  of 
dark,  organic  matter,  best 
seen  in  cross-section.     In 
metamorphic  rocks,  often 
as  rounded  or  knotty  pro- 
jections.    With    cyanite, 
sillimanite,   garnet,  tour- 
maline. 

3.5  White 
4. 

C  —  Pinacoidal,  do-        2.3      Secondary  mineral,  occur- 
matic                         2.4        ring  on  surfaces  of  rocks 
F  —  Uneven,    con-                     or  minerals  as  crystalline 
choidal                                   crusts    with    pronounced 
Brittle                                           radial,  fibrous  structure. 

3.5  White 
4. 

C  —  Basal                         2  .  6      Hardness  often  greater  due 
F  —  Splintery,    con-        2.8        to   admixture  of   quartz, 
choidal,  earthy                      feldspar;  then  tough.    De- 
Brittle                                         posits  and  veins  in  feld- 
spathic  rocks.     With  kao- 
lin, pyrite,  opal. 

3.6  White 
4.  Gray 

C  —  Rhombohedral,        2.9      Crystals  generally  curved 
perfect  (crystals)                   or  saddle-shaped   with 
F  —  Conchoidal                            pearly  luster.     Marble  in- 
Brittle                                           eludes  some  compact 
varieties.        Independent 
beds;  in  fissures  and  cav- 
ities; with  ore  deposits. 

3.5  White 
4. 

C  —  Pinacoidal,  pris-       2  .  9      Twins    common,    often 
matic,  indistinct       3.          pseudohexagonal  —  prism 
F  —  Conchoidal                           and     striated     base.     In 
Brittle                                         cracks  and  cavities;  with 
ore    deposits  ;    deposition 
from  hot  springs;  in  shells. 
With    gypsum,    celestite, 
sulphur,  siderite,  serpent- 
ine. 

530 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

1 

Color 

STRONTIANITE 
SrCO3 

250 


WITHERITE 
BaCO3 

261 


Orthorhombic  Vitreous 
C — Spear-shaped,  colum-  Transparent 
nar,    acicular,    often  to  trans- 
divergent  lucent 
M — Granular,    compact, 
fibrous,  botryoidal 


Colorless 

Gray 

White 


Orthorhombic  Vitreous 

C — Pseudohexagonal  bi-  Greasy 

pyramids  resembling  Translucent 
quartz  to  trans- 

M — Radial  fibrous,  com-     parent 
pact,  globular,  gran- 
ular, lamellar 


White 

Grayish 

Colorless 


Colemanite 
Ca2B6Oii.5H2O 

271 


Monoclinic  Vitreous  Colorless 

C — Prismatic,  highly  Dull  Milky 

modified  Transparent  white 

M — Granular,  cleavable,  to  opaque  Yellowish 

compact  white 


MAGNESITE 
MgCO3 


Hexagonal  Vitreous  Snow  white 

C — Rhombohedral,  rare     Dull  Gray 

M — Compact,    granular,  Translucent      Colorless 
resembling  unglazed     to  trans- 
porcelain    on    fresh     parent 
fracture 


246 


FLUORITE  (Fluor  spar) 
CaF2 


Cubic  Vitreous  Colorless 

C — Cubes,  alone  or  modi-  Transparent  White 

fied,  well  developed  to  trans-  Greenish 

M — Cleavable,  granular,  lucent  white 

fibrous 


239 


6.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


531 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

3.5        White                      C  —  Indistinct                 3.6      Similar  to  aragonite.     Di- 
4.                                         F  —  Uneven                      3.8       vergent   columnar   struc- 
Brittle                                           ture   and   higher  specific 

gravity  characteristic.  In 
ore  deposits;  independent 
masses.  With  galena, 
barite,  calcite. 


3.5 

4. 


White 


C — Indistinct  4.2  Crystals,  apparently  hex- 

F — Uneven  4.3  agonal  bipyramids;  mas- 

Brittle  sive,  often  radial  fibrous 

resembling     strontianite. 

but  heavier.   Usually  with 

galena. 


3.6       White 
4.6 


C — Pinacoidal,  per- 
fect, conspicu- 
ous 

F — Uneven,  c  o  n- 
choidal 

Brittle 


2.2  Transparent  crystals,  re- 
2.4  semble  those  of  datolite, 
but  softer;  compact 
masses  look  like  chalk  or 
porcelain.  With  gypsum, 
celestite,  quartz. 


3.5 
6. 


White 


C — Rhombohedral, 
perfect  (c  r  y  s- 
tals) 

F — Conchoidal, 
conspicuous 

Tough  to  brittle 


2.9  Conchoidal  fracture  gen- 
3.1  erally  prominent.  Com- 
pact varieties  are  appar- 
ently very  hard.  Dis- 
seminated in  talcose  and 
chloritic  schists,  serpen- 
tine, gypsum;  independ- 
ent beds. 


White 


C — Octahedral,  per- 
fect, conspicu- 
ous 

Brittle 


3 .  Recognized  by  crystal 
3.2  form,  octahedral  cleav- 
age, and  hardness.  Com- 
mon gangue  of  metallic 
ores,  especially  galena, 
sphalerite,  cassiterite;  also 
with  calcite,  barite. 


532 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CHABAZITE                     Hexagonal                            Vitreous            White 
C  —  Rhombohedral,  cube-  Translucent      Colorless 
CaAl2Si6Oi6.8H2O,                like;  lenticular               to  trans-          Gray 
etc.         M  —  Compact                         parent 

327 


g 

APOPHYLLITE 

Tetragonal 

Vitreous 

Colorless 

0 

C  —  Prismatic,  pyramidal, 

Pearly 

White 

w 

H14K2Ca8(Si03)16. 

pseudocubical,  tabu- 

Transparent 

Yellowish 

9H20 

lar 

to  nearly 

white 

M  —  Lamellar,    granular, 

opaque 

compact 

326 


Pectolite  (Pyroxene) 

(Ca,Na2)2(Si03)2 

307 


Monoclinic  Vitreous  White 

C — Acicular,   rarely   ter-    Silky  Grayish 

minated:  tabular         Translucent 
M — Compact  radial  to  opaque 

fibrous  aggregates 


CYANITE  (Disthene,  kyan-  Triclinic  Vitreous  White 

ite)   C — Long,    bladed,    with-  Translucent      Grayish 

Al2SiO6  out      good      termi-     to  trans-          Colorless 

nations ;    sometimes     parent 
curved  and  radially 
grouped 

M — Coarsely  bladed, 
columnar,  fibrous 
282 


Scheelite 
CaWO< 

259 


Tetragonal  Adamantine  Gray 

C — Pyramidal,  s  n/a  1 1;  Greasy  White 

more  rarely  ibabular     Transparent  Yellowish 

M — Drusy  crusts,    com-     to  trans-  white 

pact,  reniform,  gran-     lucent 

ular,  disseminated 


5.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


533 


4.         White 
6. 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Rhombohedral, 
not  conspicuous 
F — Uneven 
Brittle 


2 . 1  Generally  in  cube-like  crys- 
2 .  t  a  1  s.  Inferior  cleavage 
distinguishes  it  from  fluor- 
ite.  In  basic  igneous 
rocks.  With  analcite, 
stilbite. 


4.         White 
5. 


C — Basal,    perfect, 

conspicuous 
F — Uneven 
Brittle 


2.3  Fish-eye  opalescence  often 

2.4  observed  on  basal  pina- 
coid.     Prism    faces    ver- 
tically   striated.     In    fis- 
sures and  cavities  in  basic 
igneous  rocks.     With  na- 
trolite,  analcite,  datolite, 
native  copper,  calcite. 


4.          White 
6.          Grayish 

C  —  Basal,  ortho- 
pinacoidal 
F  —  Uneven,  fibrous 
Brittle 

2.7      Fibers   usually    divergent, 
2.8       long,     and    very    sharp. 
In  fissures  and  cavities  in 
basic  igneous  and  meta- 
morphic  rocks.    With  zeo- 
lites, datoUte. 

White 


C — Pinacoidal  per- 
fect, conspicu- 
ous 

Brittle 


3 . 5  Often  with  bluish  streaks 
3.7  or  spots  irregularly  dis- 
tributed. Hardness  varies 
with  direction,  4-5  par- 
allel to  long  direction,  6-7 
at  right  angles  thereto. 
In  gneiss,  mica  schist. 
With  staurolite,  garnet, 
corundum. 


4.6       White 


C — Pyramidal,  not 
conspicuous 

F — Conchoidal,  un- 
even 

Brittle 


5.9  Small,  well  developed  oc- 
6.2  tahedral-like  crystals, 
usually  on  quartz;  when 
massive  high  s  p  e  c  i  fi  c 
gravity  important.  With 
cassiterite,  wolframite, 
fluorite,  apatite,  molyb- 
denite. 


534 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

€olor 

Wollastonite  (Pyroxene,  tab-  Monoclinic  Vitreous  White 

ular  spar)   C — Tabular,  prismatic        Silky  Gray 

CaSiOs  M — Cleavable,  fibrous,      Transparent     Colorless 

granular,  compact         to  trans- 
lucent 


306 


APATITE 

Ca6F(P04)3 


Hexagonal  Vitreous  White 

C — Prismatic,  thick  tab-  Greasy  Gray 

ular1  Transparent     Colorless 
M — Compact,  fibrous,  to  trans- 
nodular,  reniform  lucent 


273 


HEMIMORPHITE 
H2Zn2SiO5 


280 


(Gala-  Orthorhombic  Vitreous 

mine)   C — Thin  tabular,  pyrami-  Dull 

dal,  hemimorphic,       Transparent 

highly  modified  to  opaque 

M — Compact,    globular, 

stalactitic,      fibrous, 

granular,       cellular, 

earthy 


Colorless 

White 

Gray 


SMITHSONITE 
ZnCO3 


247 


Hexagonal  Vitreous  White 

C — Small,  usually  as  Pearly  Brownish 

druses  or  crusts  Dull  white 

M — Botryoidal,  stalac-  Transparent  Gray 

titic,    granular,    eel-     to  nearly  Colorless 

lular,    fibrous,    com-     opaque 

pact 


ANALCITE   (Zeolite) 

Na2Al2(SiO3)4.2H2O 


Cubic  Vitreous  Colorless 

C  —  Tetragonal    trisocta-  Transparent  White 

hedrons,  cubes  to  nearly  Grayish 

M  —  Granular,  compact        opaque 


325 


6.     COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


535 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

4.5        White                      C  —  Basal,  ortho-            2.8      Fibers  may  be  parallel  or 

5.                                                pinacoidal                 2.9        divergent.     Typical   con- 

F  —  Uneven                                  tact     mineral     often     in 

Brittle                                           crystalline  limestone. 

With     garnet,     diopside, 

vesuvianite,  graphite. 

4.5 
5. 


White 


C — Basal,  imperfect 
F — Conchoidal,  un- 
even 
Brittle 


3 . 1  Crystals  may  be  vertically 

3 . 2  striated  and  highly  modi- 
fied.    In  crystalline  lime- 
stone; ore  deposits,  igne- 
ous rocks.     With  quartz, 
cassiterite,    fluorite,    wol- 
framite. 


4.5        White 
5. 


C — Prismatic 

F — Uneven,    c  o  n- 

choidal 
Brittle 


3 . 3  Crystals  often  in  sheaf-like 
3.5  groups  or  druses  in  cav- 
ities. When  massive  may 
be  porous.  In  limestones. 
With  sphalerite,  galena, 
and  especially  smithson- 
ite. 


5.         White 
Gray 


C — Rhombohedral, 
not  often  ob- 
served 

F — Uneven,  splint- 
ery- 
Brittle 


4 . 1  Cellular  varieties  are  called 
4.5  dry  bone.  Often  mixed 
with  sand,  clay,  limonite, 
calcite.  With  zinc  min- 
erals, especially  sphaler- 
ite, hemimorphite.  Fre- 
quently as  a  pseudo- 
morph  after  calcite. 


5. 
5.5 


White 


C — None 

F — Uneven,    c  o  n- 

choidal 
Brittle 


2.2  Good     crystals     common. 

2.3  In    fissures    and    cavities 
in    basic    igneous    rocks. 
With  apophyllite,  chaba- 
zite,     natrolite,    datolite, 
native    copper,    epidote. 


536 


B.     MINERALS  WITH  NON-METALLIC  LUSTER 


Streak    Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

Natrolite  (Zeolite)  Orthorhombic  Vitreous  White 

C — Slender  prismatic,    Silky  Colorless 

Na2Al(AlO)(SiO3)3.  nearly  square;  radial  Transparent  Grayish 

2H2O  or  interlacing  groups     to  trans- 


324 


M — Fibrous,  granular, 
compact 


lucent 


Datolite 

Ca(B.OH)Si04 


Monoclinic  Vitreous  Colorless 

C — Prismatic,  pyramidal,  Greasy  Greenish 

tabular,  highly  Dull  white 

modified  Transparent  Gray 

M — Compact  fibrous,  to  opaque 
granular,  botryoidal 


283 


NEPHELITE 


(Nepheline,  Hexagonal  Greasy  White 

elseolite)   C — Short  prismatic,  tab-  Vitreous  Bluish  gray 

ular  Transparent  Greenish  gray 

M — Compact,  dissemi-        to  opaque  Colorless 
nated  grains 


301 


SCAPOLITE  (Wernerite) 


I  raCa4Al6Si6O26 


Tetragonal 

C — Thick  prismatic, 

coarse,  often  large 
M — Compact,  fibrous, 

columnar,  granular 


Vitreous  White 

Greasy  Gray 

Translucent      Greenish  gray 


Tremolite  (Amphibole) 
CaMg3(SiO3)4 
310 


Monoclinic  Silky  White 

C — Bladed,  without  ter-  Vitreous  Yellowish 

minations  Transparent  white 

M — Compact,  columnar,  to  opaque  Colorless 

granular 


5.     COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


537 


Hardness  3  to  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.          White                      C  —  Prismatic                  2.2      Needle-like    crystals    have 

6.6                                       F  —  Uneven                     2.3        nearly    square    cross-sec- 

Brittle                                           t  i  o  n.     With  chabazite, 

analcite,  apophyllite,  stil- 

••':<ft..                                                                                           bite,  datolite. 

6. 
6.6 


White 


C — None 

F — Conchoidal,  un- 
even* 
Brittle 


2 . 9  Crystals  glassy,  often  with 
3.  greenish  tinge;  compact 
masses  resemble  wedge- 
wood  ware  or  unglazed 
porcelain;  often  with  red- 
dish, brownish,  or  yellow- 
ish streaks  and  spots. 
In  cracks  and  cavities  in 
basic  igneous  rocks.  With 
native  copper,  calcite, 
zeolites. 


White 


C — Indistinct 
F — Conchoidal,  un- 
even 
Brittle 


2.6  Distinguished  from  ortho- 
clase  by  inferior  cleavage 
and  more  greasy  luster. 
With  feldspar,  cancrinite, 
biotite,  sodalite,  zircon, 
corundum;  not  with 
quartz. 


White 


C — Prismatic  2.6      Crystals    may    appear    as 

F — Conchoidal  2.8        though    fused.       Typical 

Brittle  contact       mineral.        In 

metamorphic  rocks,  es- 
pecially granular  lime- 
stones. With  pyroxenes, 
amphiboles,  apatite,  gar- 
net, biotite. 


White 


C — Prismatic,  con-        2.9 
spicuous — 124°        3 . 1 
Brittle 


Silky  luster  and  distinct 
cleavage  (124°)  import- 
a  n  t.  Common  contact 
mineral.  In  limestones, 
dolomites,  schists. 


538 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

DIOPSIDE  (Pyroxene)            Monoclinic                           Vitreous            Gray 
C  —  Prismatic,  thick  col-  Dull                   Greenish  gray 
CaMg(SiOs)2                                 umnar,  prism               Transparent     Yellowish 
angle  87°                        to  opaque         white 
M  —  Compact,    granular,                             Colorless 
lamellar,  columnar 

305 


OPAL,  varieties 

Amorphous 

Vitreous 

Colorless 

Precious  opal 

M  —  Reniform,  botryoid- 

Pearly 

Gray 

SiO2.xH2O  Milk  opal 

al,    porous,    earthy, 

Dull 

Milk  white 

Wood  opal 

compact 

Transparent 

Yellowish 

Hyalite 

to  opaque 

white 

Silicious  sinter 

Tripolite 

232 

LEUCITE 

Pseudocubic 

Vitreous 

Gray 

C  —  Tetragonal    trisocta- 

Greasy 

White 

K2Al2Si4Oi2 

hedrons 

Translucent 

Yellowish 

M  —  Rounded  dissemi- 

to opaque 

white 

313 

nated  grains 

Streak — Uncolored,  white,  or  light  gray 


ORTHOCLASE,  Monoclinic  Vitreous  White 

varieties       C — Prismatic,  thick  tabu-  Pearly  Gray 

KAlSi3O8        Adularia          lar;  twins;  of  ten  large  Translucent      Colorless 
Sanidine  M — Cleavable,    granular,    to  trans- 
Ordinary  disseminated  parent 

03 

1 

CO 

3  316 


MICROCLINE 


KAlSi3O8 


318 


Triclinic  Vitreous  Gray 

C — Prismatic,  thick  tabu-  Pearly  White 

lar ;  twins;  often  large  Translucent  Yellowish 

M — Cleavable,    granular     to  trans-  white 

disseminated  parent 


(Feldspars  continued  on  next  page.) 


5.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


539 


Hardness  3  to  6 

Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture   =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

6.          White                      C  —  Prismatic;  con-        3.2      Prismatic,      pseudotetrag- 
6.          Gray                              spicuous    basal       3.3        onal    crystals,    with    dis- 

parting 
F — Uneven 
Brittle 


tinct  basal  parting.  May 
show  colorless  and  dark 
green  zones.  In  crystal- 
line limestones.  With 
vesuvianite,  garnet, 
scapolite,  spinel,  apatite. 


5.5 
6. 


White 


F — Conchoidal, 
conspicuous 

when  compact; 

earthy 
Brittle 


2 . 1  Precious  opal,  with  play  of 
2.3  colors;  milk  opal,  com- 
pact, milk  white;  wood 
opal,  woody  structure; 
hyalite,  resembles  drops 
of  melted  glass;  silidous 
sinter,  porous  or  botry- 
oidal;  tripolite,  earthy  and 
gritty. 


5.5       White 
6. 

C  —  Indistinct 
F  —  Conchoidal 
Brittle 

2.5 

Well  developed  crystals  or 
rounded  grains,  dissemi- 
nated in  eruptive  rocks- 
With  sanidine,  augite, 
nephelite,  olivine. 

Hardness  over  6 

6.         White 
6.5 

C  —  Basal,  c  1  i  n  o- 
pinacoidal,  con- 

2.5 
2.6 

Distinguished  from  other 
feldspars  by  rectangular 

spicuous,  90° ; 
often  step-like 

F — Conchoidal,  un- 
even 

Brittle 


cleavage  and  absence  of 
twinning  striations.  Adu- 
laria,  opalescent,  trans- 
par,ent  or  slightly  cloudy; 
sanidine,  glassy,  tabular 
or  square  crystals.  With 
quartz,  other  feldspars, 
mica,  hornblende,  zircon. 


6.          White 
6.5 


C — Basal,  brachy- 
pinacoidal,  con- 
spicuous, 90°  30' 

F — Uneven 

Brittle 


2.5  Resembles  orthoclase,  but 

2.6  with   slightly   inclined 
cleavages  and  may  show 
twinning     striations     on 
basal    pinacoid.      Occur- 
rence and  associates  same 
as  for  orthoclase. 


540 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak  —  Uncolored,  white,  or  light  gray 

Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

ALBITE 

Triclinic 

Vitreous            White 

NaAlSi3O8(Ab) 

C  —  Tabular,  twins,  small  Pearly               Gray 
M  —  Compact,  curved  or  Transparent     Colorless 
divergent                        to  trans- 
lamellar,  granular         lucent 

319 

g    g   LABRADORITE 

<   J 
S   *§       AbiAni.  .  .AbiAn3 

p  -a 

H»    * 

^s     « 

Triclinic                                Vitreous            Gray 
C  —  Thin    tabular,    often  Pearly               Greenish  gray 
with  rhombic               Translucent      White 
cross-section                   to  nearly 
M  —  Compact,  cleavable,     opaque 
granujar 

Anorthite 

Triclinic 

Vitreous            Colorless 

CaAl2Si2O8(An) 

C  —  Prismatic,  tabular        Pearly               White 
complex                        Transparent     Gray 
M  —  Compact,  cleavable,     to  trans- 
lamellar                          lucent 

322 

SPODUMENE  (Pyroxene)     Monoclinic 

C — Prismatic,  tabular, 

LdAl(Si03)2  vertically  striated 

M — Cleavable,  broad 
columnar 


Vitreous  White 

Pearly  Grayish  white 

Transparent  Greenish 
to  opaque         white 


308 


Sillimanite  (Fibrolite) 
Al2SiO6 


Orthorhombic  Vitreous  Gray 

C — Long,  thin,  needle-  Silky  Yellowish 

like  Transparent  gray 

M — Fibrous,  columnar,  to  trans-  Grayish  white 

radiating  lucent 


282 


6.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


541 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

White 


6.5 


C — Basal,  brachy- 
pinacoidal,  con- 
spicuous, 86°  24' 

F — Uneven 

Brittle 


2.6  Inclined  cleavages  often 
show  fine,  parallel  twin- 
ning striations.  Moon- 
stone, opalescent.  With 
quartz,  other  feldspars, 
mica,  chlorite,  beryl, 
rutile. 


6. 
6.5 


White 


C — Basal,  brachy- 
pinacoidal,  con- 
spicuous, 86°  4' 

F — Uneven 

Brittle 


2 . 7  Often  with  play  of  colors — 
yellow,  green,  blue,  red. 
Inclined  cleavages  are 
striated.  In  basic  igne- 
ous rocks.  With  pyrox- 
enes, amphiboles. 


6. 
6.5 


White 


C — Basal,  brachy- 
pinacoidal,  con- 
spicuous, 85°  50' 

F — Uneven 

Brittle 


2 . 7  Commonly  in  small,  glassy, 

2.8  highly  modified  crystals. 
In   basic    igneous   rocks; 
crystalline        limestones. 
With  olivine,    pyroxenes, 
pyrrhotite,  magnetite. 


White 


C — Prismatic;  pina- 
coidal  parting 
conspicuous 

F — Uneven,  splin- 
tery 

Brittle 


3 . 1  Commonly  in  broad  plates 

3 . 2  due  to  distinct  pinacoidal 
parting.    Prism  angle  93°. 
May  have  irregular 
brownish  stains.     In 
granitic  rocks.     With 
tourmaline,        lepidolite, 
beryl. 


White 


C — Macropinacoidal      3 . 2 
F — Uneven  3 . 3 

Brittle 


Crystals  often  large,  bent, 
striated,  with  rounded 
edges,  without  good  ter- 
minations, and  interlaced. 
In  metamorphic  rocks — 
mica  schist,  gneiss.  With 
andalusite,  zircon. 


542 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

CYANITE  (Disthene,  kyan-  Triclinic 


Al2SiOc 


ite)  C — Long,  bladed,  with- 
out good  termina- 
t  i  o  n  s ;  sometimes 
curved  and  radially 
grouped 

M — Coarsely  bladed, 
columnar,  fibrous 


Vitreous 

Translucent 
to  trans- 
parent 


White 

Grayish 

Colorless 


282 


ANDALUSITE 

Al2SiO5 

281 


Orthorhombic  Vitreous  White 

C — Prismatic,   r  o  u  g  h,  Dull  Pearl  gray 

nearly  square,  often    Translucent      Reddish  gray 
large,  without  termi-      to  opaque 
nations 

M — Columnar,  fibrous, 
granular,  dissemi- 
nated 


GARNET,  variety 


Cubic 


Vitreous 

Grossularite  C — Dodecahedrons,     te-  Transparent 
Ca3Al2(SiO4)3  tragonal  trisocta-          to  trans- 

hedrons,  alone  or  in     lucent 
combination 
M — Granular,    compact, 

lamellar,  dissemi- 
290  nated  grains 


Colorless 

White 

Greenish 

white 
Yellowish 

white 


QUARTZ,  Phanerocrystal-      Hexagonal 

line  varieties       C — Prismatic,  horizon- 
SiO2  Rock  crystal  tally  striated 

Milky  quartz  columnar 

Ordinary         M — Compact,  granular 


Vitreous  Colorless 

Greasy  White 

Transparent  Gray 

to  trans-  Milky 

lucent 


Cryptocrystalline  Hexagonal                            Waxy                White 

varieties  C — Never  in  crystals          Vitreous            Gray 

Chalcedony  M — Nodular,  botryoidal,  Translucent 

Agate  banded,  clouded,           to  opaque 

Onyz  concretionary,  sta- 

Hornstone  lactitic,  compact 
222              Chert 

(Quartz  continued  on  next  page.) 


5.  COLORLESS,  WHITE,  OR  -LIGHT  GRAY  IN  COLOR 


543 


6.          White 
7. 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Pinacoidal,  per- 
fect, conspicu- 
ous 

Brittle 


3.5  Often  with  bluish  streaks 
3.7  or  spots,  irregularly  dis- 
tributed. Hardness 
varies  with  direction,  4—5 
parallel  to  long  direction, 
•6-7  at  right  angles  there- 
to. In  gneiss,  mica  schist. 
With  staurolite,  corun- 
dum, garnet. 


6. 
7.5 


White 


C — Prismatic  3.1      Due  to  alteration,   surface 

F — Uneven  3 . 2        may  be  coated  with  scales 

Brittle  of  mica,  then    softer.     In 

metamorphic  rocks,  often 
as  rounded  or  knotty  pro- 
jections. With  cyanite, 
sillimanite,  garnet. 


6.6        White 
7.5 

C  —  Dodecahedral, 
usually  indis- 
tinct 
F  —  Conchoidal,  un- 
even 
Brittle 

3.4 
3.7 

Typical    contact    mineral, 
in   crystalline  limestones 
and  dolomites.    With  wol- 
lastonite,  vesuvianite,  di- 
opside,  scapolite. 

White  C — Indistinct  2.6      Characteristic      conchoidal 

F — Conchoidal,  fracture,     glassy    luster, 

conspicuous  Rock  crystal,  colorless,  or 

Brittle  nearly  so,  generally  crys- 

tallized ;  milky  quartz,  milk 
white  and  nearly  opaque. 


White 


C — Indistinct  2.6      Not  as  glassy  as  phanero- 

F — Conchoidal,  crystalline  varieties. 

conspicuous  Chalcedony,  hornstone, 

Brittle  to  tough  chert,    uniform    in    color; 

agate,  onyx,  clouded  or 
banded.  To  distinguish, 
see  reference. 


544 


B.  MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Crystallization 

Name,  Composition,  and 

Structure 

Luster 

Pnlnr 

Reference 

Crystals  =  C 

Transparency 

v^oior 

Massive  =  M 

QUARTZ  Clastic  varieties 

Hexagonal 

Vitreous 

Gray 

Sand 

M  —  Grains,  fragments, 

Dull 

White 

SiO2                Sandstone 

either  loose  or 

Translucent 

Itacolumite 

strongly  consoli- 

to opaque 

Quartzite 

dated 

222 

* 

ZIRCON 

Tetragonal 

Adamantine 

Brownish 

C  —  Square    prisms    with 

Vitreous 

gray 

ZrSi04 

bipyramids,  small, 

Pearly 

Lavender 

well  developed 

Transparent 

gray 

M  —  Irregular  lumps, 

to  opaque 

Colorless 

225 

grains 

BERYL 

Hexagonal 

Vitreous 

White 

C  —  Long  prismatic,  often 

Transparent 

Yellowish 

Be3Al2(SiO3)6 

vertically  striated, 

to  trans- 

white 

large 

lucent 

Greenish 

M  —  Columnar,  granular, 

white 

compact 

Colorless 

313 

TOPAZ 

Orthorhombic 

Vitreous 

Colorless 

C  —  Prismatic,    vertically 

Transparent 

White 

Al2(F,OH)2Si04 

striated,  highly 

to  opaque 

Grayish 

modified 

M  —  Co  ipact,    granular, 

rolled  fragments 

283 


CORUNDUM 

A12O3 


Hexagonal  Vitreous 

C — Prismatic,  tabular,       Translucent 
pyramidal,  rhombo-     to  trans- 
hedral;  rough  or  parent 

rounded  barrel- 
shaped 

M — Compact,    granular, 
lamellar 


Gray 

Greenish  gray 
Bluish  gray 


228 


5.  COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR 


545 


7.         White 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage 
Fracture 
Tenacity 

=  C 
=  F 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Indistinct  2 . 6     Sand,  loose,  unconsolidated 

F — Uneven  grains;  sandstone,  consoli- 

Brittle  to  tough  dated    sand;    itacolumite, 

flexible  sandstone;  quartz- 
ite,  metamorphosed  sand- 
stone. 


7.6       White 


C — Indistinct  4.4      In    acid    igneous    rocks — 

F — Uneven  4.8        granite;  syenite;  alluvial 

Brittle  deposits;  with  gold,  spinel, 

corundum,    garnet.     Jar- 
gon, colorless  or  smoky. 


7.6 
8. 


White 


C — Indistinct 
F — Conchoidal,  un- 
even 
Brittle 


2.6  Crystals  usually  simple — 
2 . 8  pi  ism  and  base.  In  gran- 
itic rocks,  mica  schists, 
clay  slates.  With  quartz, 
feldspars,  mica,  chryso- 
beryl,  garnet,  topaz,  tour- 
maline. 


White 


C — Basal,    perfect, 

conspicuous 
F — Conchoidal,  un- 
even 

Brittle 


3 . 4  Crystals  usually  developed 
3.6  on  one  end  only.  Mass- 
sive  varieties  distinguish- 
ed from  quartz  by  higher 
specific  gravity  and  basal 
cleavage.  In  veins  and 
cavities  in  granitic  rocks; 
alluvial  deposits.  With 
cassiterite,  tourmaline, 
fluorite,  beryl,  scheelite, 
wolframite. 


9. 


White 


C — None,  nearly 
rectangular 
basal  and  rhom- 
bohedral    part- 
ings    conspicu- 
ous; often  stri- 
ated 

F — Conchoidal 
Brittle  to  tough 


3 . 9  When  massive  often  multi- 
4 . 1  colored — blue,  green,  red, 
yellow.  In  limestones, 
granites,  syenites,  schists, 
alluvial  deposits.  With 
magnetite,  nephelite, 
mica,  spinel,  chlorite. 


546 


B.    MINERALS  WITH  NON-METALLIC  LUSTER 


Streak — Uncolored,  white,  or  light  gray 


Name,  Composition,  and 
Reference 

Crystallization 
Structure 
Crystals  =  C 
Massive  =  M 

Luster 
Transparency 

Color 

DIAMOND                               Cubic                                    Adamantine     Colorless 
C  —  Octahedrons,    hexoc-  Greasy              Gray 
C                                                     tahedrons,  usually      Transparent     White 

188 


with  curved  surfaces     to  trans- 
f    M — Rounded  or  irregular    lucent 
grains  or  pebbles, 
often  with  internal 
radial  structure 


5.    COLORLESS,  WHITE,  OR  LIGHT  GRAY  IN  COLOR  547 


10.          Ash  gray 


Hardness  over  6 


Hard- 
ness 

Streak 

Cleavage  =  C 
Fracture  =  F 
Tenacity 

Specific 
Gravity 

Characteristics  and 
Associates 

C — Octahedral,  per-       3.5      May    be    tinged    yellow, 


fect,  usually 
conspicuous 

F — Conchoidal 

Brittle 


brown,  red,  blue.  In  ser- 
pentine rocks — kimberl- 
ite,  peridotite,  called  blue 
ground;  placers;  with  py- 
rope,  magnetite,  chro- 
mite,  cassiterite,  zircon, 
gold. 


INDEX 


Names  of  minerals  described  or  referred  to  in  the  text  are  printed  in  heavy-faced 
type,  synonyms  and  names  of  varieties  in  italics,  and  general  subjects  in  light-faced 
type.  When  there  is  more  than  one  reference,  the  important  one  is  printed  in 
heavy-faced  type. 


Actinolite,  311,  466,  476 

schist,  311 
Adularia,  317,  538 
Agate,  223,  331,  456,  512,  542 

banded,  223 

clouded,  223 

moss,  223 
Agricola,  G.,  xii 
Airy's  spirals,  122 
Alabandite,  207 
Alabaster,  264,  520 
Albite,  81,  86,  87,  319,  331,  359,  540 

law,  320 

Alexandrite,  271,  331,  484 
AUanite,  287,  388,  426,  432 
Allochromatic,  88 

Almandite,  292,  331,  392,  434,  456,  510 
Aloxite,  340 
Altaite,  214 
Aluminates,  267 
Aluminum,  minerals,  339 

tests  for,  170 

-uranium,  362 
Alum  stone,  262,  448,  528 
Alundum,  235,  340 
Alunite,  262,  339,  357,  448,  528 
Amazonite,  318,  331 
Amazonstone,  318,  331,  478 
Amethyst,  222,  331,  456,  482 

oriental,  229,  330,  456,  484 
Ammonal,  340 
Ammonium,  test  for,  171 
Amorphous,  96 

Amphibole,  77,  309,  312,  339,  343,  349, 
351,  388,  424,  432,  462,  466, 
476,  494,  536 

Analcite,  21,  326,  359,  450,  534 
Analyzer,  104 


Andalusite,  281,  331,   339,  454,  520,  542 

Andesine,  319 

Andesite,  139 

Andradite,  292,  331,  392,  434,  456,  480, 

510 

Angles,  constancy  of,  1 
Anglesite,  257,  350,.  526 
Anhydrite,  xiii,  254,  343,  430,  468,  524 
Aniso  tropic,  102 
Anorthic  system,  78 
Anorthite,  322,  343,  540 
Antimonite,  204 
Antimony,  gray,  204 

minerals,  341 

tests  for,  171 

Apatite,  45,  273,  343,  348,  356,  428,  430, 
450,  472,  496,  500,  504,  522,  526, 
534 

chloro,  274 

fluor,  274 
Aplite,  139 

Apophyllite,  61,  326,  357,  448,  532 
Aquamarine,  314,  330,  482 
Aragonite,  70,  86,  87,  249,  343,  502,  528 

test  for,  169 

Argentite,  21,  213,  358,  396 
Arizona  ruby,  292,  331,  332 
Arkose,  140 
Arsenic,  194,  341,  398,  404 

minerals,  341 

tests  for,  171 
Arsenical  gold  ore,  204 
Arsenides,  202,  203 
Arsenopyrite,  71,  211,  341,  349,  404 
Asbestos,  311,  464,  494,  516 

amphibole,  311,  464,  494,  516 

chrysotile,  298,  464,  494,  516 

longfibered,  311,  464 

short  fibered,  298,  311,  464 
Assembly  of  blowpipe  apparatus,  147 


549 


550 


INDEX 


Asterism,  89 

Asymmetric  system,  78 

Augite,  307,  388,  424,  432,  464,  478 

Auripigment,  204 

Aventurine,  222,  331,  456,  512 

Axes,  crystallographic,  3 

of  symmetry,  11 

optic,  102 

dispersion  of,  120 
Axial  ratio,  6 
Axinite,  81 
Axis,  brachy,  65,  78 

clino,  72 

intermediate,  30 

lateral,  30 

macro,  65,  78 
.     ortho,  72 

principal,  30,  55 
Azurite,  252,  331,  347,  462 
Azurmalachite,  253 


Barite,  71,  256,  342,  468,  470,  498,  522, 

524 
Barium,  minerals,  342 

tests  for,  172 
Bar  theory,  237 
Barytes,  256 
Basal  pinacoid,  75 
Basalt,  139 

Bauxite,  235,  339,  438,  486,  518 
Baveno  law,  86,  316 
Bauer,  M.,  329 
Bead  tests,  163 
Becke,  F.  J.,  106 

method,  105 
Beryl,  38,  313,  330,  339,  342,  482,  514,  544 

golden,  313 

yellow,  313 
Beryllium,  minerals,  342 

tests  for,  172 
Biaxial  crystals,  102,  116 

behavior  in  polarized  light,    171 

figures,  118,  119 

Biotite,  294,  349,  351,  382,  428,  468 
Bipyramid,  ditetragonal,  57 

hemi,  73 

hexagonal,  first  order,  32 
second  order,  33 
third  order,  43 

orthorhombic,  66 

tetra,  78 


Bipyramid,  tetragonal,  first  order,  56 

second  order,  57 
Birefringence,  102 
Bismuth,  195,  342,  402,  408 

flux,  147 

reactions  with,  153,  157 

minerals,  342 

tests  for,  172 
Bismuthinite,  205 
Bisphenoids,  tetragonal,  62 
Black  jack,  205,  384,  430 

sand,  249 
Blanc  fixe,  342 
Blende,  205 

zinc,  205 

Bloodstone,  223,  331 
Blowpipe,  145 

apparatus,  145,  147 

methods,  145 

portable  outfit,  150 

reactions,  152 

reagents,  147 
Blue  ground,  189 

stone,  266 

vitriol,  266,  460,  468 
Bog  iron  ore,  235,  488 
Boracite,  26 
Borates,  267 
Borax  bead,  147 

reactions  with,  163 
Bornite,  216,  347,  349,  408,  420 
Boron,  minerals,  343 

tests  for,  173 
Bort,  188,  191,  438 
Bortz,  188,  191 
Boule,  337 

Bournonite,  217,  341,  347,  350,  396 
Brachy,  axis,  65,  78 

bipyramid,  67 

dome,  68 
hemi,  79 

prism,  67 

Brazilian  law,  85,  221 
Breccia,  141 
Breithauptite,  208 
Brilliant  cutting,  190 
Brimstone,  193 
Brochantite,  263,  347,  460 
Broggerite,  262 
Bromine,  tests  for,  173 
Bronzite,  304,  476,  506 
Brush,  G.  J.,  145 
Bytownite,  319 


INDEX 


551 


Cadmium,  tests  for,  173 
Cairngorm  stone,  222,  331 
Calamine,  247,  280,  504,  534 
Calcite,   xiii,   41,    82,   83,84,    135,  242, 
343,    344,   428,   446,   468,   498, 
518,  524 

test  for,  169 
Calcium,  minerals,  343 

tests  for,  173 
Cole  spar,  242 
Californite,  288,  331 
Cancrinite,  302,  359,  506 
Cape  ruby,  292,  331,  332 
Carbon,  minerals,  345 

tests  for,  174 
Carbonado,  188,  192,  438 
Carbonates,  241 
Carbuncle,  292,  331 
Camelian,  223,  331,  456 
Carnotite,  277,  362,  363,  486 
Cassiterite,  85,  226,  361,  392,  418,  426, 
434,  444,  454,  492,  510 

test  for,  169 

Cat's  eye,  222,  271,  331,  482,  484,  512 
Celestite,  255,  360,  472,  524 
Center  of  symmetry,  12 
Cerargyrite,  238,  358,  492,  516 
Cerium,  minerals,  346 

test  for,  174 

Cerussite,  251,  350,  500,  526 
Chabazite,  42,  327,  448,  532 
Chalcanthite,  266,  460,  468 
Chalcedony,  223,  331,  436,  482,  512,  542 
Chalcocite,  214,  347,  249,  396 
Chalcopyrite,  64,  215,  347,  406,  410 
Chalcotrichite,  232 
Chalk,  244,  518 

French,  299,  518 
Chalybite,  248 
Charcoal  support,  146 

reactions  on,  156 
Chemical  formulas,  125 

calculation  of,  125 
Chert,  224,  542 
Chessylite,  252 
Chiastoiite,  281 
Chile  saltpeter,  241,  494,  520 
China  clay,  301,  518 
Chloanthite,  210 
Chlorine,  tests  for,  174 
Chlorite,  297, 339, 351, 382, 422, 460,  466 


Chondrodite,  286,  348,  351,  454,  508 

Chromates,  254 

Chrome  iron,  270 

Chromite,  270,  346,  349,  388,  426 

Chromium,  minerals,  346 

tests  for,  175 

Chrysoberyl,  271,  331,  339,  342,  484,  516 
Chrysocolla,  293,  331,  347,  460,  466,  468 
Chrysolite,  289,  480 
Chrysoprase,  223,  331,  482 
Chrysotile,  298,  464,  494 
Cinnabar,  53,  54,  215,  354,  412,  438 
Cinnamon  stone,  292,  330 
Citrine,  222,  331 
Civilization  and  mineralogy,  ix 
Class,  dihexagonal  bipyramidal,  3 

ditetragonal  bipyramidal,  55 

ditrigonal  pyramidal,  46 
scalenohedral,  38 

dyakisdodecahedral,  27 

hexagonal  bipyramidal,  42 

hexoctahedral,  14 

hextetrahedral,  22 

monoclinic  prismatic,  73 

orthorhombic  bipyramidal,  65 

pinacoidal,  78 

tetragonal  scalenohedral,  61 

trigonal  trapezohedral,  50 
Classes,  of  crystals,  13 

of  symmetry,  13 
Clausthalite,  214 
Cleavage,  93 
Cleveite,  262 
Clino-axis,  72 

dome,  74 

hemi-bipyramid,  74 

pinacoid,  75 

prism,  74 

Clinochlorite,  297,  382,  422,  460,  466 
Clinorhombic  system,  72 
Clinorhomboidal  system,  78 
Clinozoisite,  287 
Closed  tube,  146 

reactions  in,  165 
Cobalt,  glance,  210 

minerals,  347 

nitrate,  148 

test  for,  175 

Cobaltite,  210,  341,  347,  404 
Coefficients,  rationality  of,  7 
Cog  wheel  ore,  217,  316 
Colemanite,  271,  343,  530 
Colloids,  96 


552 


INDEX 


Color,  of  minerals,  88 

change  of,  89 

play  of,  89 
Colored  screens,  161 
Colors,  interference,  112 
Columbates,  272 

Columbite,  273,  349,  353,  355,  392,  400 
Columbium,  test  for,  175,  179 
Combination,  6 
Conglomerate,  141 
Congruent,  23 
Cooperite,  364 

Copper,    21,    97,    135,    196,     347,    408, 
412 

blue  carbonate  of,  252 

green  carbonate  of,  252 

minerals,  347 

nickel,  208 

plush,  232 

shot,  197 

tests  for,  175 
Copperas,  266,  466,  520 
Copper  ore,  gray,  218 

horse  flesh,  216 

purple,  216 

ruby,  232 

yellow,  215 
Coquina,  244,  524 
Corundum,  42,  228,  330,  339,  394,  402, 

424,  458,  484,  516,  544 
Covellite,  215 
Critical  angle,  101 
Crocoite,  258,  346,  350,  440 
Cross,  axial,  3 

Cryolite,  240,  339,  348,  359,  522 
Qyptocrystalline,  96 
Crystal,  aggregate,  96 

form,  5 

systems,  4 

Crystalline  aggregate,  96 
Crystallization,  elements  of,  7 
Crystallography,  xiv,  1 

subdivisions  of,  1 
Crystalloids,  96 
Crystals,  xiii 

classes  of,  13 
Cube,  16 

pyramid,  18 
Cubic  system,  14,  372 
Cuprite,  232,  347,  416,  442 
Cupro-titanium,  362 
Cyanite,  282,  331,  339,  472,  480,  532,  542 
Cymophane,  271,  331 


Dana,  J.  D.,  186 

Datolite,  283,  331,   343,   450,  474,  536 

Dauphine  law,  85,  221 

Deltoid,  23 

Desmine,  326 

Demantoid,  292,  331 

Dialtage,  306 

Diamond,  188,  330,  345,  438,  544 

cutting  of,  190 

matura,  226 

Diamonds,  famous,  191 
Diaphaneity,  95 
Diatomaceous  earth,  234 
Dichroic,  122 
Didodecahedron,  27 
Dihexagonal,  bipyramid,  34 

bipyramidal  class,  31 

prism,  37 
Dimorphism,  130 
Diopside,  305,  331,  476,  538- 
Diorite,  139 
Diploid,  27 
Dispersion,  100 

of  diamond,  100 

of  glass,  101 

of  optic  axes,  120 
Disthene,  282,  472,  480,  532,  542 
Distortion,  2 
Ditetragonal,  bipyramid,  57 

prism,  59 
Ditrigonal,  prisms,  47,  52 

pyramidal  class,  46 

pyramids,  46 

scalenohedral  class,  38 
Dodecahedron,  pentagonal,  27 

rhombic,  16 

trigonal,  24 

Dogtooth  spar,  243,  498,  524 
Dolerite,  139 

Dolomite,  141,  245,  343,  344,  351,  500, 
528 

test  tor,  169 
Dome,  68 

brachy,  68 

clino,  74 

hemi-brachy,  79 
-macro,  79 
-ortho,  75 

macro,  69 
Dry  bone,  247 
Dyakisdodecahedron,  27 


INDEX 


553 


Dyakisdodeeahedral  class,  26 
Dysluite,  268,  394,  436 


E 


Earth,  diatomaceous,  234 

infusorial,  234 
Elaeolite,  301,  474 
Elements,  187 

of  crystallization,  7 

of  symmetry,  10 
Emerald,  314,  330,  482 

oriental,  229,  330,  484 
Emery,  228,  394,  402,  428 
Enargite,  219,  341,  347,  398 
Endlichite,  275 
Enstatite,  304 

Epidote,  286,  331,  339,  343,  349,  434, 
480,  510 

rock,  287 

schist,  287 
Epsomite,  265,  520 
Etch  figures,  24 
Exolon,  340 


Faces,  regular  position  of,  12 
Fayalite,  289 
Feel,  95 

Feldspar,  316,  316,  331,  339,  432,  452, 
478,  508,  538 

glassy,  317 

lime,  322 

lime-soda,  321 

plagioclase,  319,  540 

potash,  316 

soda,  319 
Ferberite,  261,  349,  362,  386,  398,  416, 

424,  490 
Ferrites,  267 
Perromanganese,  353 
Ferro-titanium,  362 
Ferro-uranium,  362 
Fibrolite,  282,  508,  540 
Flame,  colorations,  160 

oxidizing,  150 

reducing,  150 

structure  of,  150 
Flint,  224,  436,  512 
Flossi  ferri,  240 
Fluorine,  minerals,  348 

test  for,  176 


Fluorite,  21,  84,  93,  135,  239,  343,  348, 

448,  472,  504,  530 
Fluorspar,  239,  448,  472,  504,  530 
Fool's  gold,  208 
Form,  closed,  5 

crystal,  5 

fundamental,  5 

modified,  5 

negative,  24 

open,  5 

positive,  24 
Forms,  congruent,  23 

enantiomorphous,  51 

relationship  of,  20,  38,  60 
Forsterite,  289 
Fowlerite,  309 
Fracture,  94 
Franklinite,  21,  270,  349,  353,  363,  390, 

400 

Freibergite,  218 
Fuchsite,  296 
Fusibility,  scale  of,  151 


Gabbro,  139 

Gahnite,  268,  394,  436,  484,  514 

Galena,  20,  21,  212,  350,  396,  404 

Galenite,  212,  396,  404 

Gangue,  136 

Garnet,  21,  290,  330,  339,  343,  349,  392, 

434,  456,  480,  510,  542 
Garnerite,  300,  351,  354,  460,  466 
Gels,  96 
Gems,  329 

cutting,  333 

methods  of  identification,  332 

synthetic,  337 

weight  of,  333 
Geode,  136 
German  silver,  355 
Gersdorffite,  210 
Geyserite,  234 
Glaucodote,  212 
Glossary,  366 
Glucinum,  test  for,  172 
'Gneiss,  141 
Gold,  200,  348,  406,  408 

free  milling,  201 

minerals,  348 

ore,  arsenical,  204 

placer,  200 

tests  for,  176 
Goldschmidt,  V.,  11 


554 


INDEX 


Granite,  xii,  138 
Graphite,  192,  345,  394,  422 
Greenockite,  208 
Greisen,  227 

Grossularile,  292,  330,  456,  482,  510,  542 
Groth,  von,  P.  H.,  128 
Guano,  274 

Gypsum,  77,  86,  264,  331,  343,  344,  444, 
494,  520 


Halite,  21,  24,  93,  236,  444,  496,  520 
Haloids,  236 
Hardness,  90 
Hauerite,  210 

Hausmannite,  253,  353,  386 
Hauy,  R.,  8 

Heliotrope,  223,  331,  456,  482 
Hematite,  41,   230,  331,  349,  382,  390, 
412,  414,  438 

argillaceous,  230,  390,  414,  440 

black,  253 

brown,  235 

compact,  230,  390,  414,  440 

fossiliferous,  231,  438 

oolitic,  231,  438 

specular,  230,  382,  390 
Hemi-bipyramid,  73 

clino,  74 

ortho,  74 
Hemi-dome,  brachy,  79 

macro,  79 

ortho,  79 

Hemimorphite,  280,  363,  504,  534 
Hemiprism,  79 
Hemiprismatic  system,  72 
Hercynite,  268,  394,  428 
Hessite,  214 
Hessonite,  292,  330 

Hexagonal,    bipyramid,    first   order,    32 
second  order,  33 
third  order,  43 

bipyramid  al  class,  42 

prism,  first  order,  36 
second  order,  36,  49 
third  order,  43 

pyramid,  second  order,  48 

system,  30,  373 
Hexagonite,  310 
Hexahedron,  16 
Hexoctahedral  class,  14 


Hexoctahedron,  18 

Hextetrahedral  class,  22 

Hextetrahedron,  24 

Hiddenite,  308,  331 

Hornblende,  312,  388,  424,  432,  462,  476 

Horn  silver,  238,  492,  516 

Hornstone,  542 

Huebnerite,  260,  353,  362,  386,  416,  424, 

430,  442,  450,  490,  504 
Human  activity,  divisions  of,  ix 
Hyacinth,  226,  331 
Hyalite,  233,  538 
Hydrobromic  acid,  148 
reactions  with,  155 
Hydrogen,  test  for,  176 
Hydroxides,  219,  232 
Hypersthene,  304,  331 


Ice,  219 

stone,  240 

Iceland  spar,  243,  524 
Icositetrahedron,  17 
Idiochromatic,  88 
Umenite,  303,  349,  361,  388,  400 
Indices,  Miller's,  10 
Infusorial  earth,  234 
Invar,  355 
Iodine,  tests  for,  176 
Idocrase,  288 
Iridescence,  89 
Iron,  minerals,  349 

spathic,  248 

tests  for,  177 
Iron  ore,  bog,  236,  412,  414,  488 

chrome,  270 

fossiliferous-,230,  412 

magnetic,  268 

oolitic,  230,  412 

red,  230 

specular,  230 

titanic,  303 

yellow,  235,  406 

Iron  stone,  brown  clay,  235,  412,  414,  486 
Isinglass,  295,  496,  522 
Isodimorphism,  130 
Isometric  system,  14 
Isomorphism,  128 
Isotropic  substance,  102 

behavior  of  in  polarized  light,  110 
Itacolumite,  224,  544 


INDEX 


555 


Jacinth,  226,  331 
Jade,  311,  331 
Jadeite,  311,  331 
Jamesonite,  218 
Jargon,  226,  331 
Jasper,  223,  456,  512 
Jolly  balance,  91 


Kaolin,  301,  492,  518 

Kaolinite,  301,  339,  492,  518 

Karlsbad  law,  86,  316 

Keene's  cement,  344 

Kunz,  G.  F.,  332 

Kunzite,  308 

Kyanite,  282,  472,  480,  534,  542 


Labradorescence,  321 

Labradorite,  321,  331,  432,  478,  540 

La  Croix,  A.,  187 

Lamprophyre,  139 

Land  plaster,  265 

Lapis  lazuli,  303,  331,  462,  474 

Laterite,  235 

Lautarite,  241 

Lazurite,  303,  331,  359,  360,  462,  474 

Lead,  black,  192,  394,  422 

glance,  212 

minerals,  350 

are,  white,  251 

tests  for,  177 
Lemberg's  test,  169 
Lepidolite,  297,  348,  351,  444,  446,  522, 

526 

Lepidomelane,  294 
Leucite,  313,  339,  357,  538 
Leucitohedron,  17 
Light,  observations  in,  104 

polarized,  107 

reflection  of,  99 

refraction  of,  99 

total  reflection  of,  101 
Limestone,  141,  243,  428,  498 

oolitic,  98 

Limonite,  235,  349,  386,  406,  412,  414, 
486,  488 

compact,  235,  414 

ochreous,  236 


Liquids,  immersion,  106,  107 
Lithium,  minerals,  351 

tests  for,  177 
Lionite,  340 
Lithophone,  342 
Lodestone,  268,  269 
LSllingite,  212 
Luster,  88 

M 

Macro-axis,  65,  78 

bipyramid,  67 

dome,  69 
hemi,  79 

prism,  67 
Magnaleum,  352 
Magnesia  alba,  352 
Magnesite,  246,  351,  530 
Magnesium,  minerals,  351 

tests  for,  178 
Magnetism,  93 
Magnetite,  21,  268,  349,  402 
Malachite,  252,  331,  347,  462 

matrix,  252 

Mannebach  law,  86,  316 
Manganese,  black  oxide,  227 

minerals,  353 

tests  for,  178 

Manganite,  97,  234,  353,  384 
Manganites,  253 

Marble,  xii,  142,  244,  428,  498,  524 
Marcasite,  211,  349,  406,  410 
Marialite,  322 
Mart,  244,  518 
Martite,  230,  390 
Materials,  source  of,  ix 
Matura  diamond,  226 
Meerschaum,  300,  520 
Meigen's  test,  169,  243,  250 
Meionite,  323 
Melanite,  292 

Melanterite,  266,  349,  466,  520 
Menaccanite,  303,  404 
Mercury,  minerals,  354 

tests  for,  178 
Merwin  color  screen,  146 

observations  with,  161 
Miargyrite,  218 
Mica,  293,  339,  357 

"A",  295 

amber,  294 

black,  294,  382,  428 


556 


INDEX 


Mica,  bronze,  294,  446 

lithium,  297,  444,  446,  522 

magnesium,  294 
-iron,  294 

potash,  296 

ribbon,  295 

rwted,  295 

wedge,  295 

wMfe,  295 
Micanite,  296 
Michel-Levy,  A.,  138 
Microcline,  318,  331,  357,  478,  538 
Microcosmic  salt  bead,  147 

reactions  with,  163 
Microscope,  centering  of,  104 

polarizing,  103 
Miller,  W.  H.,  10 

indices,  10 
Millerite,  208 
Mineral,  definition  of,  xiii 

resources,  10 
Mineralogy,  and  civilization,  xi 

chemical,  14 

descriptive,  xiv,  186 

determinative,  xiv 

divisions  of,  xiv 

history  of,  xii 

physical,  xiv 

relation  to  other  sciences,  xi 
Minerals,  xii 

accessory,  137 

classification  of,  186,  339 

decomposition  of,  143 

determination  of,  379 

essential,  137 

formation  of,  131 

names  of,  126 

occurrence,  134 
Mispickel,  211 
Molybdates,  254 
Molybdenite,  206,  354,  394,  402 
Molybdenum,  minerals,  354 

tests  for,  179 

Monazite,  272,  346,  356,  452,  506 
Monel,  355 

Monoclinic  system,  72,  377 
Monoclinohedral  system,  72 
Monosymmetric  system,  72 
Moonstone,  317,  320,  331 
Morganite,  314,  330 
Muscovite,  89,  295,  496,  522 


N 


Nail-head  spar,  243,  498,  524 
Natrolite,  324,  359,  506,  536 
Nepheline,  301,  474,  536 
Nephelite,    301,    339,    357,    359,     474, 

536 

Nephrite,  311,  331 
Niccolite,  208,  341,  354,  410,  420 
Nichrome,  355 
Nickel,  minerals,  354 

tests  for,  179 
Nicol  prism,  109 
Niobium,  minerals,  355 

test  for,  179 
Nitrates,  240 
Nitrogen,  minerals,  355 

tests  for,  180 
Nivenite,  262 


Oblique  system,  72 
Ocher,  brown,  235,  412,  486 

red,  230,  412,  438 

yellow,  235,  406,  486 
Octahedron,  16 
Odor,  95 
Oligonite,  249 

Olivine,  289,  331,  349,  351,  480 
Onyx,  223,  331,  436,  542 

marble,  245 

Opal,  232,  331,  358,  452,  478,  492,  508, 
518,  538 

fire,  233,  331,  452 

jasper,  233,  452,  508 

milk,  233,  538 

precious,  233,  331,  508,  538 

wood,  233,  508,  538 

resin,  233 
Opalescence,  89 
Open  tube,  146 

reactions  in,  164 
Ore,  kidney,  231 
Orpiment,  204,  341,  486 
Orthite,  287,  343,    346,   349,    388,   426, 

432 
Ortho,  axis,  72 

hemi-bipyramid,  74 

pinacoid,  75 

prism,  74 

Orthoclase,  77,  86,  134,  316,  331,  357, 
452,  508,  538 


INDEX 


557 


Orthorhombic,  bipyramid,  66 
bipyramidal  class,  65 
system,  66,  376 

Oxides,  219 

Oxygen,  tests  for,  108 


Parameters,  4 

Parana etral  ratio,  4 

Paramorphs,  143 

Parting,  94 

Paste,  188 

Patronite,  363 

Pearceite,  218 

Pearl  spar,  245 

Pectolite,  307,  359,  532 

Pegmatite,  139 

Pencil  rock,  264 

Penfield,  S.  L.,  125 

Pentagonal  dodecahedron,  27 

regular,  27 
Pentlandite,  207 
Pericline  law,  87,  320 
Peridot,  289,  331,  480 
Perthite,  321 
Petzite,  214 

Phlogopite,  294,  351,  446,  496 
Phosphate  rock,  273,  428,  430,  496,  500, 

522,  526 
Phosphates,  272 
Phosphorus,  minerals,  356 

tests  for,  180 

Picotite,  268,  394,  408,  492 
Pinacoid,  59 

basal,  37,  69,  75,  79 

brachy,  69,  79 

clino,  75 

macro,  69,  79 

ortho,  75 

Pinacoidal  class,  78 

Pitchblende,  262,  384,  398,  414,  420,  422 
Placers,  136 

Plagioclase,  319,  343,  359,  540 
Planes  of  symmetry,  10 
Plaster  of  Paris,  265 
Plaster  tablet,  146 

reactions  on,  152 
Platinum,  195,  356,  402 

minerals,  356 

tests  for,  180 
Pleochroism,  122 
Pleonaste,  268,  394,  436,  484,  514 


Plumbago,  192,  394,  422 
Pneumatolysis,  133 
Polar,  23 
Polarized  light,  107 

by  absorption,  107 

by  reflection,  108 

by  refraction,  108 

circular,  120 

convergent,  110 

observations  in,  123 

parallel,  110  | 

Polarizer,  104 
Polybasite,  218 
'Polymorphous,  130 
Potash  salts,  238 
Potassium,  minerals,  357 

test  for,  181 
Precious  stones,  239 

cutting  of,  333 

methods  of  identification,  332 

synthetic,  337 

weight  of,  333 
Prism,  brachy,  67 

clino,  74 

ditetragonal,  59 

hemi,  79 

hexagonal,  first  order,  36 
second  order,  36 
third  order,  43 

macro,  67 

ortho,  74 

tetragonal,  first  order,  59 
second  order,  59 

dihexagonal,  37 

ditrigonal,  47,  52 

trigonal,  47 
Prismatic  system,  65 
Prochlorite,  297,  382,  422,  460,  466 
Proustite,  217,  341,  358,  412,  440 
Pseudomorphs,  143,  144 
Pseudosymmetry,  57 
Psilomelane,  253,  353,  388,  400,  426 
Pycnometer,  92 
Pyramidal  system,  55 
Pyramid  tetrahedron,  24 
Pyrargyrite,  217,  341,  358,  382,  412,  440 
Pyrolusite,  227,  353,  396 
Pyrite,  25,  29,  84,  208,  331,  349,  408,  410 
Pyrites,  copper,  215 

iron,  208,  408,  410 

magnetic,  207 

spear,  211 

white  iron,  211,  406,  410 


558 


INDEX 


Pyritohedron,  27 

Pyromorphite,  275,  350,  356,  462,  472, 

490,  502 

Pyrope,  292,  331,  351,  456 
Pyroxene,  77,  304,  307,  331,  343,  349, 

351,   388,   424,   432,   452,   464, 

476,   478,   506,   508,   532,   538, 

540 
Pyrrhotite,  207,  349,  410,  420 


Q 


Quadratic  system,  55 
Quartz,  xiv,  53,  54,  82,  83,  85,  134,  136, 
220,  331,  358,  436,  456,  482,  512, 
542,  544 

cap,  221 

clastic,  222,  224 

cryptocrystalline,  222,  223 

crystalline,  222 

ferruginous,  222,  456,  512 

granular,  224 

milky,  222,  542 

rose,  222,  331,  456 

rutilated,  222,  331 

scepter,  221 

smoky,  222,  331,  436,  512 
Qaartzite,  142,  224,  456,  512,  544 


R 


Rammelsbergite,  212 
Ratio,  axial,  6 

parametral,  4 

Rationality  of  coefficients,  7 
Realgar,  203,  341,  438 
Refraction,  double,  101 
character  of,  116 
strength  of,  112,  116 

index  of,  100,  105,  111 

single,  99 

Refractometer,  Smith's,  332 
Regular  system,  14 
Relationship  of  forms,  20,  38,  60 
Relief,  106 

Rhodochrosite,  248,  353,  448 
Rhodolite,  292,  331 
Rhodonite,  309,  331,  353,  452,  508 
Rhombic,  dodecahedron,  16 

system,  65 

Rhombohedron,  39,  50 
Rhyolite,  139 
Rock  crystal,  222,  331,  542 


Rocks,  xii,  137 

dike,  139 

extrusive,  138 

igneous,  137 

intrusive,  138 

metamorphic,  141 

plutonic,  138 

sedimentary,  140 

volcanic,  138 
Roscoelite,  296,  363 
Rubeilite,  284,  331,  332,  458 
Rubicelle,  268,  330,  458 
Ruby,  228,  330,  456 

Arizona,  292,  331,  332 

cape,  292,  331,  332 

Rutile,  61,  224,  361,  392,  418,  426,  434, 
444,  454,  490,  510 


S 


Safflorite,  212 
Salt,  common,  236 

epsom,  265,  520 

rock,  236,  444,  496,  520 
Salt  of  phosphorus,  147 

reactions  with,  163 
Sand,  224,  456,  512,  544 

black,  269 

Sandstone,   xii,   140,  224,  456,  512,  544 
Sanidine,  317,  538 
Sapphire,  228,  330,  484 

golden,  229 

white,  229 

yellow,  229 
Sard,  223,  331,  456 
Satin  spar,  264,  331,  494,  520 
Scalenohedron,  40 

tetragonal,  62 
Scapolite,  332,  339,  343,  359,  452,  476, 

536 

Scheelite,  259,  343,  362,  504,  532 
Schists,  142 
Schwatzite,  218 
Seienite,  264,  494,  520 
Selenium,  test  for,  181 
Sepiolite,  300,  351,  520 
Sericite,  296 
Serpentine,  135,  297,  331,  351,  430,  470, 

500 

Shale,  140 
Siderite,  248,  349,  384,  414,   422,  488, 

502 
Silicates,  277 


INDEX 


559 


Silicon,  minerals,  358 

tests  for,  181 

Sillimanite,  282,  339,  508,  540 
Silver,  98,  199,  358,  382,  402 

glance,  213,  396 

horn,  238,  492,  516 

minerals,  358 

tests  for,  181 
Silver  ore,  dark  ruby,  217 

light  ruby,  217 
Sinter,  calcareous,  244 

silicious,  234,  508,  538 
Slate,  142 

Smaltite,  135,  210,  341,  347,  404 
Smith  refractometer,  332 
Smithsonite,  247,  363,  474,  506,  534 
Snow,  219 

Soapstone,  299,  464,  494,  518 
Sodalite,  303,  339,  359,  474 
Soda  niter,  241,  355,  359,  494,  520 
Sodium,  carbonate,  147 

reactions  with,  158 

minerals,  359 

tests  for,  181 
Sorel  cement,  351 
Spar,  calc,  242 

dog-tooth,  243,  498,  524 

heavy,  256,  468,  470,  498,  522,  524 

Iceland,  243,  524 

Labrador,  323,  331 

nail-head,  243,  498,  524 

pearl,  245 

satin,  264,  331,  494,  520,  524 

tabular,  306,  534 
Spathic  iron,  248 
Spear  pyrites,  211 
Specific  gravity,  90 
Spectroscope,  160 
Specular  iron  ore,  230,  382,  390 
Spelter,  207 
Sperrylite,  210 

Spessartite,  292,  331,  353,  456,  510 
Sphalerite,  25,  26,   135,  205,  363,    384, 
414,  422,  430,  442,  448,  488,  502 
Sphene,  323,  331,  384,  450,  474,  -506 
Spiegeleisen,  353 

Spinel,  21,  267,  330,  339,  349,  351,  394, 
426,  436,  456,  484,  492,  514 

Betas,  268,  458 

blue,  267,  330,  484 

law,  84 

ruby,  268,  330,  458 
Spodumene,  308,  331,  339,  351,  540 


Stalactite,  245,  428,  498,  524 

Stalagmite,  245 

Staurolite,  85,  279, 331, 339, 349, 436, 514 

Steatite,  299,464,494,518 

Stellite,  347 

Steno,  N.,  2 

Stephanite,  218 

Stibnite,  204,  341,  396,  404 

Stilbite,  326,  359,  446,  500,  526 

Stones,  precious,  329 

semi-precious,  330 
Strass,  188 
Streak,  89 

plate,  89 

Stromeyerite,  214 
Strontianite,  250,  360,  502,  530 
Strontium,  minerals,  360 

tests  for,  182 
Structure  of  minerals,  96 
Sulphates,  254 
Sulphides,  202,  203 
Sulpho-minerals,  202,  215 
Sulphur,  70,  193,  360,  494,  496 

minerals,  360 

tests  for,  182 
Syenite,  xii,  139 
Sylvite,  24 
Symmetry,  axes  of,  11 

center  of,  12 

classes  of ,  13 

classification  of,  372 

elements  of,  10 

planes,  10 
Synthetic  gems,  337 
System,  anorthic,  78 

asymmetric,  78 

clinorhombic,  72 

clinorhomboidal,  78 

crystal,  4 

cubic,  14,  372 

hemiprismatic,  72 

hexagonal,  30,  373 

isometric,  14 

monoclinic,  72,  377 

monoclinohedral,  72 

monosymmetric,  72 

oblique,  72 

orthorhombic,  65,  376 

pyramidal,  55 

prismatic,  65 

quadratic,  55 

regular,  14 

rhombic,  65 


560 


INDEX 


System,  tesseral,  14 
tessular,  14 
tetragonal,  55,  375 
triclinic,  78,  378 
trimetric,  65 


Talc,  299,  351,  464,  494,  518 
Tantalite,  273,  392,  400 
Tarnish,  89 
Taste,  95 

Tellurium,  tests  for,  182 
Tenacity,  94 
Tennantite,  218 
Tesseral  system,  14 
Tetra-bipyramid,  78 
Tetragonal,  bipyramid,  first  order,  56 
second  order,  57 

bisphenoid,  62 

prism,  first  order,  59 
second  order,  59 

scalenohedral  class,  61 

scalenohedron,  62 

system,  55,  375 
trisoctahedron,  17 

tristetrahedron,  23 
Tetrahedrite,  26,  218,  341,  347,  349,  354, 

358,  363,  384,  398 
Tetrahedron,  22 
Tetrahexahedron,  18 
Thermite,  340 
Tiger's  eye,  223,  331 
Tin,  minerals,  361 

stone,  226 

stream,  226,  418 

tests  for,  183 

wood,  226,  418 
Titanates,  277 
Titanite,    323,  331,  343,  361,  384,  432, 

450,  474,  506 
Titanium,  minerals,  361 

tests  for,  183 
Topaz,  71,  283,  330,  339,  348,  514,  544 

false,  222,  331,  512 

oriental,  229,  330,  516 

precious,  283 

Spanish,  222,  331,  512 
Topazolite,  292,  331 
Touch,  95 

Tourmaline,  50,  284,  331,  339,  343,  351, 
392,  436,  458,  482,  512 

sun,  284 


Trachyte,  139 

Transparency,  95 

Trapezohedron,  trigonal,  51 

Travertine,  244,  428,  498,  524 

Tremolite,  310,  536 

Triboluminescence,  206 

Trichroic,  123 

Triclinic  system,  78,  378 

Trigonal,   bipyramid,   second  order,   50 

prism,  first  order,  46 
second  order,  52 

pyramid,  first  order,  46 

trapezohedral  class,  50 

trapezohedron,  51 

trisoctahedron,  17 

tristetrahedron,  23 
Trimetric  system,  65 
Trimorphous,  130 
Tripolite,  234,  492,  508,  518,  538 
Trisoctahedron,  tetragonal,  17 

trigonal,  17 
Tristetrahedron,  tetragonal,  23 

trigonal,  23 
TroUite,  207 
Troostite,  289,  508 
Tufa,  calcareous,  244,  428,  498,  524 
Tungstates,  254 
Tungsten,  minerals,  362 

tests  for,  183 

Turquois,  276,  331,  339,  356,  464,  478 
Turkey  fat,  247 
Twin  crystals,  122 


U 


Ullmannite,  210 

Ultramarine,  native,  303 
Uniaxial  figure,  115 

substance,  102 

behavior  of,  110,  113 
Uralite,  307,  312 
Uralization,  312 
Uranates,  254 

Uraninite,  262,  362, 384, 398, 414, 420, 422 
Uranium,  minerals,  362 

tests  for,  184 
Uvarovite,  292,  331,  480 


Vanadates,  272 

Vanadinite,  275,  350,  363,  440,  446,  488, 
489 


INDEX 


561 


Vanadium,  minerals,  363 

tests  for,  184 
Veins,  135 
Verd-antique,  298 
Vermilion,  natural,  215 
Vesuvianite,  61,  288,  331,  339,  343,  348, 

480,  510 
von  Groth,  P.  H.,  128 


Wulfenite,  259,  350,  354,  440,  446,  488, 

498 
Wurtzite,  208 


Yellow  ammonium  sulphide,  149 
reactions  with,  153 


Water,  219 

Wavellite,  276,  339,  356,  472,  500,   528 

Weisbach,  A.,  90 

Wernerite,  322,  452,  476,  536 

White  lead  are,  251 

Wfflemite,  289,  363,  478,  508 

Witherite,  251,  342,  530 

Wolfachite,  212 

Wolframite,'    261,    349,    353,    362,    386, 

389,  416,  420,  424,  442,  490 
Wollastonite,  306,  534 
Wood,  opal,  233,  508 

tin,  226,  418 
Wright,  F.  K,  104 


Zeolite,  needle,  324 

Zeolites,  324,  339,  343,  448,  450.  500,  506, 

526,  532,  534,  536 
Zinc,  blende,  205 

minerals,  363 

ore,  red,  228 

tests  for,  184 

Zincite,  228,  363,  416,  442,  490 
Zircon,  61,  225,  331,  364,  458,  514,  544 
Zirconium,  minerals,  364 

tests  for,  185 
Zoisite,  287 
Zwitter,  227 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

EARTH  SCIENCES  LIBRAFT 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
Renewed  books  are  subject  to  immediate  recall. 


General  Library 

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LD  21-40TO-5/65 
(F4308slO)476 


JUN2     1951 


653 


